May Kohanim visit Kivreiy Tzaddikim?
Many Poskim rule it is forbidden for Kohanim to visit the gravesite of Tzaddikim. Nevertheless many Kohanim are lenient in this, especially with regards to visiting their Rebbe’s Kever. Practically a Kohen may not to be lenient in this and so is the vintage Chabad custom and the practical directive given by the Rebbe. Kohanim that desire to merit the advantage of praying by the gravesite of a Tzaddik are to stand a distance from the cemetery or grave, in view of the grave and pour their hearts to Hashem from there.
Mearas Hamachpeila: It is permitted for Kohanim to visit the burial site of the forefathers in Chevron known as the Mearas Hamachpeila, and so is the practical custom. However there are opinions that are stringent.
Rashbi: Kohanim are not to enter into the building of the Tziyon of Rashbi in Meiron. Likewise care must be taken while ascending the mountain to walk only through the special path for Kohanim. However some Poskim are lenient as stated above.
The Rebbe’s Ohel: The Ohel of the Rebbe is set up in a way that allows Kohanim to access the Ohel through a special path that contains dividers of ten Tefach on each side. It is forbidden for Kohanim to extend their hand past these dividers. The Kever itself is unroofed and is surrounded by a short wall [of at least ten Tefach] which is a distance of at least four Tefach from the grave. This allows the Kohanim to stand anywhere near the wall. It is permitted for them to stand even in the front area of the Kever where the tomb stone is found. Nevertheless care must be taken not to extend the hand past the wall surrounding the Kever. Thus when throwing the Pan one is to do so from behind the wall or give it to a friend to do so. May they touch the wall?
 For a thorough analysis on this subject see: Nitei Gavriel Aveilus 2/91; Shulchan Menachem 5/330; Ishkavta Direbbe p. 103; Koveits Beis Ahron Veyisrael 76 p. 116 and the sources mentioned there.
The Ramban [Emor] states that “those which pass away through Neshika do not give off impurity, as only those that die due to the bite of the Nachash have impurity. This then is the meaning that Tzaddikim don’t give impurity.” This is likewise brought in the Zohar [Vayishlach 168]; Chinuch Mitzvas 263; Panim Yafos Chukas; A similar statement is brought in Midrash Mishleiy 9/2 that Eliyahu Hanavi [who is a Kohen] buried Rebbe Akiva. When asked by Rebbe Yehoshua on what basis did he allow himself to become deal with the corpse Eliyahu replied “by my life Rebbe Yehoshua my son, G-d forbid, Tzaddikim do not have impurity and neither do their students.” However the Tosafus [Bava Metzia 114b] explains that in truth the real allowance was because Rebbe Akiva was considered a Meis Mitzvah. Alternatively, says Tosafus, Eliyahu was not a Kohen at all, but rather from the children of Rachel. Certain
 Halachos Ketanos 1/177; Pischeiy Teshuvah 372/2; Alef Lamagen 581/111; Peas Hashulchan 2/18; Kitzur SHU”A 202/14; Tuv Taam Vadaas 2/231; Netza Shorek 108; Sheiris Yehuda [brother of Baal Hatanya] Miluim 35; Igros Kodesh 11/220; 6/348; Likkutei Sichos 18/234 [brought in Shaareiy Halacha Uminhag 3/150; Shulchan Menachem 5/330] Shaareiy Tzedek by Chayeh Adam; Divrei Yichezkel 1; Zayis Rana 2/27; Rav Shmuel Salanat [is Biblical prohibition], brought in Tzitz Eliezer 10/1; Iskavta Direbbe p. 103; See Sdei Chemed Asifas Dinim Eretz Yisrael; Aveilus; Rosh Hashana that majority of Achronim which he brings are stringent.
The reason: As the burial site of Tzaddikim do give off impurity. [Tosafus Bava Metzia 114b]
 To touch the grave is a Biblical prohibition. [Rambam Tumas Meis 2/15; Sheiris Yehuda ibid] To be within four Amos of the grave is a Rabbinical prohibition. [Michaber 371/5; Sota 44a] To be within the same building as the grave [Ohel] is a Biblical prohibition. [Rambam Tumas Meis 2/15; Michaber 371/1] If however the Kever is surrounded by a Golel and Dofek [a covering
 Brought in Sdei Chemed ibid; Shaareiy Halacha Uminhag ibid; The following Poskim justify the practice of those Kohanim that visit the gravesite of a Tzaddik: Minchas Elazar 3/64 based on Arizal; Mahrsha Alfandri 1/23; Pnei David of Chida; Igara Dekala Behaloscha [brought in Nitei Gavriel ibid] that so is the custom of Kohanim in Eretz Yisrael; Sheiris Yehuda ibid mentions that the custom in Eretz Yisrael is to visit the gravesite of the Tanaaim, however he explains the reason is because it was built with Poseiach Tefach and hence the Tuma does not spread.
The reason: The burial grounds of Tzaddikim do not give off Tuma. [Ramban Emor; Zohar Vayishlach 168; Chinuch Mitzvas 263; Panim Yafos Chukas; Midrash Mishleiy 9/2] Alternatively we assume the Aron is built in a way that the Tuma escapes [Poseiach Tefach] and there are Poskim that say the impurity today is only Rabbinical and hence for the great Mitzvah of Hishtatchus we are lenient. [Minchas Elazar ibid]
Opinion of Arizal: There is a story recorded of the Arizal sending a student which was a Kohen to Daven by the gravesite of one of the Tanaim. The Minchas Elazar ibid uses this as a proof that it is allowed to do so. See Nitei Gavriel ibid for a list of Poskim who argue that
 Alef Lamagen ibid; Nitei Gavriel 91/1 that the Poskim conclude it is forbidden.
 Teshuvah of the Mahril [printed in Hatamim 6/38; Shut Sheiris Yehuda Hosafos 35] writes that it is a Biblical prohibition even if the person is a Tzaddik Gamur, and only regarding the Rabbinical prohibition of being near [within 4 Amos] of the grave can one be lenient due to the great Mitzvah of going to Kivrei Tzaddikim. However even regarding this matter he concludes that one is to fix whatever is able to be fixed and hence he directed that in Haditch a Mechitza is to be established to allow Kohanim to come to the Ohel even Rabbinically. In Lubavitch the Ohel had signs stating “until here may Kohanim walk”. [Rebbe ibid; Ishkavta Direbbe ibid]
 Letters printed in Shulchan Menachem ibid and Shaareiy Halacha Uminhag ibid based on Teshuvah of the Mahril and so directed the Rebbe that a Mechitza be built surrounding the Ohel of his father in law. [Ishkavta Direbbe ibid] See also Likutei Sichos 18/234 footnote 55; Hisvadyus 1951/172; Sichas Yud Shavt 1954
 Alef Lamagen 581/11; Certainly their prayers will be answered in merit of the Tzaddik just as if they were standing near the grave itself. [ibid]
 This is based on a known tradition handed down from many generations. The reason for the allowance is because the Avos are buried inside a cave within a cave in a way that does not give off impurity. [Heard from Rav Asher Lemel Cohen and that so was the custom of his father [a great Gaon and Posekin Jerusalem] Rav Avraham Hersh; See Yoreh Deah 371/1; Rambam Tumas Meis 20/1] See Igros Kodesh 11/220 that although in general a Kohen may not enter near the grave of Tzaddikim, regarding entering specific gravesites of Tzaddikim one is to verify by trustworthy people that have a tradition in this matter. Rav Yaakov Bloy zatzal of the Eida Hachareidis stated that many are lenient regarding these areas. [Koveits Beis Ahron Veyisrael 76 p. 116]
 Minchas Elazar 3/64 based on Baba Basra 58a [There it states that the Kevarim of the Avos were marked to beware Kohanim from the area]
The reason: As the head of Esav, which was Jewish Heretic, was buried there, and he certainly gives off impurity. However the Tzaddikim themselves don’t give off impurity. [ibid] The Admur of Satmar was stringent like this opinion. [Koveitz Beis Ahron Veyisrael ibid]
 Heard directly from Rav Asher Lemel Cohen and that so was the custom of his father [a great Gaon and Posek in Jerusalem] Rav Avraham Hersh Cohen [unlike that which was printed in his name in Beis Ahron Veyisrael ibid]; Nitei Gavriel 91/2 that so is the ruling of most Gedolei Yisrael [Admurim of Belz; Stamar; Lubavitch; Rav moshe Fienstein; Minchas Yitzchak; Rav SZ”A.] Zayis Rana 2/27; Rav Shmuel Salanat [is Biblical prohibition], brought in Tzitz Eliezer 10/1; Nisivei Am [Minhagei Yerushalayim Beis Keil] 372; Yalkut Yosef 7/281 in name of Yabia Omer and Yechaveh Daas
 See Tzitz Eliezer 16/18 [Many Gedolim allowed Kohanim to visit Kever Rachel]; See Nitei Gavriel Aveilus 2/91-2 footnote 3 for opinions that allowed going to Kever Rachel; Rav Yaakov Bloy zatzal of the Eida Hachareidis stated that many are lenient regarding these areas. [See Koveits Beis Ahron Veyisrael 76 p. 116] There it states that
 Nitei Gavriel 91/2 that so is the ruling of most Gedolei Yisrael [Admurim of Belz; Stamar; Lubavitch; Rav moshe Fienstein; Minchas Yitzchak; Rav SZ”A.]
The Rebbe’s opinion: As stated above, the Rebbe [Igros Kodesh 11/220] writes that every individual Kever requires a particular tradition regarding it. Regarding the Tziyon in Meiron Rav Naftali Hakohen Rot relates that when he had his first private audience with the Rebbe the Rebbe asked him if he enters into the Tziyon of Rashbi. When he answered affirmatively the Rebbe wondered at this with a great exclamation. The Rebbe then asked him why he does so and he did not reply. The Rebbe said that perhaps there is a special arraignment by the Tziyon to allow Kohanim, such as an Ohel within an Ohel. Nonetheless from that point and on Rav Naftali Rot stopped entering into the Tziyon in Meiron. [Koveitz Beis Ahron Veyisrael ibid]
 As there are unknown graves buried in many areas of the mountain.
 See Nitei Gavriel Aveilus 2/91-2 footnote 3 that many Kohanim have a tradition that it is permitted to enter and that so was practiced by many Kohanim of esteemed lineage; Torah scholarship and knowledge of Kabala. See there for the opinions that defend the practice of going into the Tziyon. I heard from Rav Asher Lemel Cohen that Kohanim may enter into the building as there is a tradition that the Tziyon was built in a way which allows the impurity to escape [Poseiach Tefach] and hence there is no status of an Ohel.
 This is a recent development. In prior times access was made either through driving a car until the Ohel [Ohel Zaruk-see Igros Kodesh 6/348] or having Leviim and Yisraelim surround the Kohen, hence forming a Mechitza. [See Igros Kodesh 3/342; Hiskashrus 884] Later on a special box of ten Tefach high that surrounded the Kohanim would be used to enter through the path until the Tziyon. Recently a Mechitza was put up on both sides hence dividing the path from the impurity of the cemetery completely.
 Hence avoiding the prohibition of an Ohel for the Kohanim.
 Yoreh Deah 371/5; Igros Kodesh 6/348; Ishkavta Dirrebe p. 106
The Michaber ibid states that although it is [Rabbinically] forbidden for a Kohen to be within four Tefachim of a Kever, nevertheless if it is surrounded by a wall of ten Tefach high then one is only required to distance oneself four Tefach from the Kever.
 As when the Tomb stone was built it was distanced more than four Tefach from the body and hence it acts as part of the Mechitza to allow Kohanim to be next to it. [Heard from Rav Asher Lemel Kohen who verified the matter through those in charge of the Ohel.]
 Harav Asher Lemel Cohen; the Rebbe would direct Kohanim to be careful regarding these last two matters. [Hiskashrus 884]
 See Rama 371 /5 that one may touch walls of house.