In a corporate dispute with 50/50 shares, can an injunction be imposed on the active client list?

Injunctions which prevent a party from doing something while the case is litigated, known as preliminary injunctions, are difficult to obtain.  In order to obtain a preliminary injunction in NY state court, the moving party has to show (a) a likelihood of success on his/her claim on which the injunction is based; (b) irreparable harm absent the injunction; and (c) that the equities balance in his/her favor.  If successful, the moving party would also have to post a bond to secure the other party against any damages suffered from the injunction if it ultimately turns out that it should not  have been issued. You have not stated what the dispute is about, but I will assume (because it is so common) that one shareholder (not clear whether this is a corporation with shareholders, a partnership with partners, an limited liability company, with members, or something else; I'll assume it's a corporation for simpicity's sake) wants to leave the corporation and compete with it. In general, the law favors free competition, but there are a number of exceptions.  Whether this person would be allowed to compete depends on a number of factors which your question does not address.  For example, does this person currently have a position with the corporation and, if so, what is it?  Did this person sell an interest in the corporation to the other shareholder?  Is there an agreement  between the person who seeks to compete and either the corporation and/or the other shareholder which restricts the person's right to compete?  If so, how broad is that restriction (these types of restrictive covenants are not favored and will not be enforced if overbroad, although they are more likely to be enforced as applied to an owner of a closely held business than to a mere employee.)  Is the customer list a trade secret, or are the names of potential customers readily available from public information?  Etc. Assuming that the moving party can show a likelihood of success on his/her claim that the other party has no right to compete with the corporation, it is likely that a balance of the equities in the moving party's favor will also have been shown.  Since unfair competition damages the goodwill of the business, which has been held to constitute irreparable harm the second prong of the test will also have been met.  The key is whether there is a likelihood of success on the merits of the claim.