The answer to this question depends on a lot of factors, particularly whether you - the former employee - were governed by any written non-solicitation agreement barring such activity. And even if you did sign such an agreement, the answer to the question may hinge upon whether your agreement is enforceable as a matter of New York law (it very well may not be enforceable), and even if it is enforceable, there may be a question as to whether you were active or passive in the client's decision to leave your former employer.