choshen mishpat civil law - Is an ex-employee allowed to work with the customers of his former employer?

Shimon works for Business A, he has access to the contact information of all the clients and is responsible for interacting with them. Moreover, he knows how much each client is paying for Business A's products and services, as well.

Shimon leaves Business A and opens his own Business B that operates in the same field. Shimon wants to use all the information he collected on his former clients to attract those clients to his business.

Can this behavior be considered a"steal" Halachicly?

If yes, can he be sued in Beis Din and what can be the verdict?