May a man and a group of women be alone together?
*Important note: There are several circumstances that can break a Yichud prohibition between a man and women, such as a Shomer, child, wife/husband in area. Pesach Pasuach to public, etc. The following law does not come to negate any of these valid Yichud breakers, and exclusively refers to a case that other Yichud breakers are not in place, and if the fact that many women are present can be a Yichud breaker in its own right.
A. Stringent approach-Sephardim:
It is [Rabbinically] forbidden for a man to be alone with a group of women [irrelevant of number, even 100, and so is the ruling of the Sephardim]. [This applies whether the man is a Jew, or gentile, and applies whether amongst the group of women there are gentiles.]
B. Lenient approach-Ashkenazim:
Some Poskim rule it is Rabbinically forbidden for a single man to be alone even with a group of many women, as stated above. However, other Poskim rule that a man be alone with many women, so long as the man is not accustomed to work with women. [Practically, it is best to initially be stringent and apply one of the other Yichud breakers, although in a time of need, one may be lenient.]
How many women is “many”? The definition of “many women” is defined as no less than three women. [Thus, even according to the lenient opinion, it is forbidden for a man to be alone with two women. The above number of three women, suffices during the day while one is in the city, however, at night, or when traveling out of the city, one is to initially require there to be four women present, as explained in the Q&A section.]
Qualifications of the above allowance: As stated above, even according to the lenient opinion, it is only permitted for a man to be alone with a group of women if the man is not accustomed to work with women [as defined in the Q&A]. [Likewise, it only applies if he is not overly acquainted with all the women in the group.] If, however, the man does work with women [or is overly acquainted with all of them], then it is forbidden according to all. [Some Poskim rule that the above leniency applies even if the man, or women, are not modest [i.e. Parutz], and thus it is permitted even with a gentile man, or with women who dress immodestly.]
It is forbidden for a Sefaradi man to be alone with a group of women, or a group of Sefaradi women to be alone with a man, unless one of the valid Yichud breakers are applicable.
Yichud of man and two women: Is forbidden, unless one of the valid Yichud breakers are applicable.
Yichud of man and three women or more: In a time of need, one may be lenient to allow a man to be alone with three women, even if no other Yichud breakers are applicable, if the man does not work with women for his occupation. However, at night, or on the road outside of the city, it is initially best to have four women present.
What is the definition of a man who works with women?
This matter is unclear from the Poskim. Some explain that it applies to anyone who has a job with female clientele, coworkers, or employees, of which he deals with on a constant basis. [Thus, a bus driver or taxi driver, and many jobs today would be excluded from the above allowance.] Others, however, limit this definition only to a man whose main clientele is specifically women, such as a jeweler, or man who works in a female clothing store. [Accordingly, a bus driver, or taxi can driver is included in the above allowance.] One who is defined as “working with woman” may not be alone with a group of women who he is not acquainted with.
How many women must be present at night or during travel?
Even according to the lenient opinion, some Poskim rule that it is only permitted to be with three women during the day, and not while traveling outside of the city, however at night, or during travel, three women does not suffice. Rather, in such a case, there needs to be four women present. However, some Poskim rule that at night it is forbidden for a man to be alone with any number of women, even according to the lenient opinion above. Other Poskim however suggest that even at night, or on the road, three women suffice. Practically, one may be lenient in a time of need, even if there are only three women present.
May a group of women/girls have a male bus/cab driver?
In any situation in which there aren’t other Yichud breakers applicable [i.e. husband in city; other men on bus; daytime and there is traffic], then it is forbidden for Sefaradi women/man to be on the bus. Likewise, initially, even Ashkenazi women are to be stringent. However, in a time of need, Ashkenazi women may be lenient so long as there are at least four women on the bus at all times, and so is the accustomed practice. Thus, while a group of at least four Ashkenazi women may be lenient to hire a male driver to take them somewhere, Sefaradi women, or a Sefaradi bus driver, may not do so unless they prearrange another Yichud breaker to take effect. Thus, by organized trips that will be traveling late at night, or early morning, or through deserted areas, it is best for them to arrange that either the driver’s wife comes with them [if they are Jewish], or that other men be on the bus.
May a man sleep in a home of only women?
Initially, one is not to do so. However, in a time of need, one may be lenient if there are at least four women present in the home, and the man does not work with women and is not overly acquainted with all of them.
 See Even Haezer 22:5; Dvar Halacha 10:1-2; Nitei Gavriel 21; “The Laws of Yichud” [Dubov] 1:20
 Michaber E.H. 22:5; 1st opinion in Tur 22; Rambam Issurei Biyah 22:8; Tosafus Kiddushin 82a; Dvar Halacha ibid in name of following Rishonim and Achronim: Ramban, Ritva, Semak, Aguda, Kol Bo, Mordechai in name of Riy, Rashal, Chida; Taharas Yisrael 22:15; Maharsham 3:152; 1st opinion in the following Poskim: Levush 22, Chochmas Adam 126:20, Kitzur SHU”A 152:3, Aruch Hashulchan 22
 See Pischeiy Teshuvah 22:4 in name of Shev Yaakov 19 that Biblical Yichud is only one with one; Nitei Gavriel 21 footnote 14
 So is ruling of Michaber ibid, and the Sefaradim accepted upon themselves the rulings of Maran; Heard from Harav Yaakov Yosef Z”l; Nitei Gavriel ibid
 The reason: As Nashim Daatan Kalos and can come to sin even if there are many women there. [See Rashi Kiddushin 80b]
 Noda Beyehuda E.H. Kama 69, brought in Pischeiy Teshuvah 22:4; Shevet Halevi 5:202; See Nitei Gavriel 21:5
Other opinions: Some Poskim rule that if one of the women is a gentile, then it is permitted for the man and group of women to be alone. [Erech Shaiy 22:5; See Shev Yaakov 19, brought in Pischeiy Teshuvah 22:4; Dvar Halacha 10:2]
 Poskim ibid in A; There are many Ashkenazi Poskim, Rishonim and Achronim [recorded in previous footnotes], who either rule like this opinion, or record it equally with the second opinion brought next. Hence, this opinion also has weight even for those who follow the rulings of the Rama, brought next.
 Opinion in Rama ibid; 2nd opinion in Tur 22 in name of Rashi Kiddushin 82a; Bach 22, brought in Chelkas Mechokeik 22:8; Tosafus Riy Hazakein Kiddushin 80b; Semag Lavin 126; Rashba 1:1175; Meiri Kiddushin ibid; Tosafus Rosh; Ovadia Bartenura; Mahariy Levi 18; Divrei Chaim 2:16; Divrei Malikeil 4:102; 2nd opinion in the following Poskim: Levush 22, Chochmas Adam 126:20, Kitzur SHU”A 152:3, Aruch Hashulchan 22
 The reason: As the women are embarrassed to sin in front of the others, as certainly the man will not sin with all the women, and thus there is fear that the matter will become publicized. [See Rosh ibid; Poskim ibid]
 Taharas Yisrael 22:15; Maharsham 3:152; Igros Moshe E.H. 4:65-14; Shevet Halwevi 3:183; Nitei Gavriel 21:2; “The Laws of Yichud” [Dubov] 1:20
 Chelkas Mechokeik 22:8; See also Beis Shmuel 22:8
 Mishneh Kiddushin 80b; This applies even if the man if Kosher [Rashba 1:1178; Meiri Kiddushin 80b] and even if the women are modest. [Yad Rameh Kiddushin ibid; Nitei Gavriel 21:1]
 Chochmas Adam 126:4 regarding Libo Gas Ba; Dvar Halacha 10:4 that if he is not overly acquainted with even one of the women, even though he is acquainted with the remaining women, then it is permitted.
 Dvar Halacha 10:2-3 in name Rashba, Radbaz; See there for other opinions
 See Dvar Halacha 10:7
 Nitei Gavriel 22:3
 Nitei Gavriel 22:2 footnote 4 in name of Rashba 1178; Chidushim Kadmonim on Kiddushin ibid; Toras Hayichud 3:16; See however Minchas Ish 3:11
 See Rama 22:5 regarding a woman being with many men, that at night or during travel, we are more stringent; So rules regarding travel: Pnei Yehoshua Keddushin 80b; So rules regarding night: Tosefes Chaim E.H. 22; See Igros Moshe E.H. 4:65-20 who leans to permit even trhee at night, although concludes to be stringent unless it is a time of need; Nitei Gavriel 21:7
 Pnei Yehoshua ibid regarding travel [however, not regarding night]; Tosefes Chaim E.H. 22 regarding night; Dvar Halacha 10:6 regarding night; See Nitei Gavriel 21:7 footnote 18
 Bach 22 that so applies even according to Rashi ibid; Pnei Yehoshua ibid regarding night; Misgeres Hashulchan 152:8
 Divrei Malkiel 4:102; Igros Moshe E.H. 4:65-20; Implication of Beis Yehuda E.H. 13; Dvar Halacha 10:6 regarding on the road that so is implied from Rameh, Rashal, Taz, and Chochmas Adam, however regarding at night he is stringent to require 4; See Shevet Halevi 5:202; Nitei Gavriel ibid
 Igros Moshe ibid; Nitei Gavriel 21:7 is lenient in a time of need to suffice with three women even at night
 Heard from Harav Yaakov Yosef Z”l based on the above rulings; See also Nitei Gavriel 21:3 that if the drivers wife is present, Yichud is broken, and 21:4 that if one of the woman’s husband is present, Yichud is broken,
 As a) we suspect for the first opinion initially; b) Perhaps a bus driver is defined as “Isko Im Nashim” and is hence forbidden even according to the lenient opinion.
 See Beis Yehuda E.H. 13