WASHINGTON—Toyota Motor Corp and Honda Motor Co on Saturday sharply criticized a proposal by Democrats in the U.S. House of Representatives to give union-made electric vehicles in the United States an additional $4,500 tax incentive. Toyota said in a statement that the plan unveiled late Friday discriminates “against American autoworkers based on their choice not to unionize.” The bill, set to be voted on Tuesday by the Democratic-led House Ways and Means Committee as part of a proposed $3.5 trillion spending bill, would benefit Detroit’s Big Three automakers, which have union-represented auto plants. In a statement, Honda called the bill “unfair” and said it “discriminates among EVs made by hard-working American auto workers based simply on whether they belong to a union. … The Honda production associates in Alabama, Indiana and Ohio who will build our EVs deserve fair and equal treatment by Congress.” The proposal, estimated to cost $33 …