Q: I am a partner in a firm. Can I do private work, outside of the practice?
A: Partners are required to act in accordance with their partnership agreement. Therefore if the initial understanding was that the partners would work only on behalf of the partnership, you may not take on private work. Even if the agreement does not restrict private work, you may not use the partnership’s assets for private business or work privately in a manner that impinges upon your responsibilities to the partnership (C.M. 176:10).
Nonetheless, if one partner did private work, even if he shouldn’t have, the earnings are his. However, if he used the partnership’s assets for additional business, he must share the profits (C.M. 176:11; Shach 176:22).
Additionally, one partner may not sell his share to a third party without the other partners’ consent, unless the decision-making control will remain with the initial partners, but if he did do so, the sale is valid (C.M. and Kessef Hakodashim 176:10; Aruch Hashulchan 176:50; Pischei Choshen, Shutfim 1:32).