DETROIT (Reuters) - U.S. union United Auto Workers' leaders on Friday approved a tentative four-year contract with Fiat Chrysler Automobiles NV , sending the proposed pact to 40,000 workers for a ratification vote. The move follows Fiat Chrysler workers' rejection last week of a previous tentative contract. A new tentative agreement was reached on Wednesday night, averting a call by the UAW to have its members strike Fiat Chrysler’s U.S.