Melacha and Business:
It is forbidden for the Chasan to do Melacha or business in the marketplace throughout the period of Simcha [three or seven days depending on Besula/Beula as explained in A].
Mechila/Receving permission from Kallah to do Melacha: The above prohibition applies even if the Kallah is Mochel on her Simcha, and allows him to do Melacha and go to work. [However, some Poskim rule that his applies only if the Kallah is a Besula, if however the Kallah is a Beula, then she can forgive her honor and he may go to work. Likewise, some Poskim are lenient to allow a Chasan to perform Melacha in the privacy of his home if the Kallah is Mochel, even if she is a Besula.]
May the Kallah do Melacha during the Sheva Brachos?
May the Chasan/Kallah do Melacha in order to prevent monetary loss?
Q&A on definition of Melacha
What is defined as Melacha?
May a Chasan tie Tzitzis to his new Tallis during Sheva Brachos?
May a Chasan/Kallah write during Sheva Brachos?
May one’s business partner run the business during Sheva Brachos?
May a Chasan/Kallah cut nails during Sheva Brachos?
 Michaber and Rama 64/1
 The reason: As a) He is obligated to rejoice his wife. And b) A Chasan is like a king. [Chelkas Mechokek 64/2]
 Chelkas Mechokek 64/2 and Beis Shmuel 64/2 in explanation of the novelty of Rama ibid who repeats the same ruling of Michaber that a Chasan may not do Melacha; Hamakneh, brought in Pischeiy Teshuvah 64/3; Aruch Hashulchan 64/5; Kitzur SHU”A 149/12; Poskim in Nitei Gavriel 56 footnote 2
Other Poskim: Some Poskim rule it is permitted for the Kallah to be Mochel and have her Chasan do work. [Chida in Shiyurei Bracha 64 and Chaim Sheol 2/38-Samech]
 The reason: As a Chasan is like a king and hence may not do Melacha just like a King, irrelevant of the Kallah’s permission. [Chelkas Mechokek 64/2]
 Hamakneh, brought in Pischeiy Teshuvah 64/3; Aruch Hashulchan ibid
 The reason: As only when one marries a Besula is he called a true Chasan in his own right that is similar to a king. [ibid]
 See Dovev Meisharim 3/47; Nitei Gavriel 56/2
 The reason: As a king is only forbidden from doing Melacha in public, and hence if the wife is Mochel, neither reason is relevant to prohibit the Chasan from doing Melkacha in private. [ibid]
 Michaber 342/1; Shach 342/11; Taz 342/5; Kneses Hagedila 342/1; Masas Binyamin 19; Tur 342; Ramban in Toras Hadam; Rabbeinu Yerucham 22/2; Rosh; Poskim brought in Nitei Gavriel 56 footnote 20; Yabia Omer E.H. 4/8
Other opinions: Some Poskim rule the Chasan is forbidden in getting a haircut or laundry during Sheva Brachos. [Bach Y.D. 342, brought in Shach ibid; Maharibil 3/72 according to Raavad; Kerem Shlomo 64, brought in Pischei Teshuvah 64/1] The Shach ibid strongly negates his opinion, as it argues against all the above Rishonim and Poskim. See Nitei Gavrile ibid footnote 21
 The reason: As a king needs to look beautiful, and have a nicely trimmed haircut and laundered and ironed clothing. [Shach ibid; Taz ibid]
 Nitei Gavriel 56/3 footnote 4 in name of Meiri Kesubos; Rashal Kesubos 12 and other Poskim
 Yifei Lalev 64/5; Meishiv Halacha 2/66; Sheol Umeishiv Mahdurah 5/91See Rashi Kesubos 47a
 Nitei Gavriel ibid in name of Maharsham 3/206k
 Nitei Gavriel 56/4
 Beis David Y.D. 177; Chaim Veshalom 2/27; Ben Ish Chaiy Shoftim 16; Kinyan Torah 3/32
 Daas Kedoshim 342/1; Dovev Meisharim 3/47; Chazon Ish E.H. 64/7; See Minchas Elazar 2/57
 Nitei Gavriel 56/5-6
 Levushei Mordechai E.H. Tinyana 56
 Chida in Shiyurei Bracha 64/1; Chaim Sheol 2/38; Chaim Falagi in Chaim Veshalom 2/57
 Sheilas Yaavetz 2/185
 Nite Gavriel 56 footnote 12
 See Nitei Gavriel 56/7; Mishneh Halachos 9/223; Tzitz Eliezer 11/85
 Zekan Aaron 215; Perach Mateh Ahron 2/65, brought in Pischei Teshuvah 64/1Chaim Sheol 2/38 Samech; Ben Ish Chaiy Shoftim 16; Aruch Hashulchan 64/3; Nitei Gavriel 64/8 footnote 17
 See Levushei Mordechai Tinayna 56; Nitei Gavriel 57/10
 The reason: As even on Yom Tov it is permitted to perform Melacha of Ochel Nefesh.
 Michaber Y.D. 342/1 regarding a haircut and certainly this would apply regarding nails; Nitei Gavriel 64/11