Many big companies are pushing to cut spending on employee benefits—from pensions to health insurance—and could face labor strikes as a result.

In all, major employers have about 400,000 union workers whose contracts are up for negotiation this year. They include the Detroit auto makers, whose workforces have a combined 140,000 members of the United Auto Workers; a group of railroad operators including CSX Corp., with 142,000 union employees; and telecom companies like Verizon Communications Inc., which is in talks with about 40,000 wireline workers.