After McGill, Klein studied law at the Université de Montréal, where instruction was in French. He was a law partner first of Max Garmaise, whom he followed briefly to Rouyn, a small mining development in the North of Quebec. Then, back in Montreal, he joined with Samuel Chait (who was to become first president of the Federated Zionist Organization of Canada, when it was reorganised in 1967). Klein, Garmaise, and Chait had all been officers of Young Judea, a Zionist youth organization.