Union contracts for 40,000 AT&T workers expire at midnight Saturday, putting the company at risk of a strike.
The workers are on the local-phone and long-haul data side of the business, and located mainly in the Midwest and California.
AT&T and the Communications Workers of America say negotiations are continuing. When the last big batch of contracts was negotiated three years ago at AT&T, the parties kept talking past the contract expiration, and there was no strike.
AT&T has 256,000 employees, of which slightly more than half are unionized. That makes it the country's largest private employer of union labor.
At issue in the negotiations are job protection clauses and health care premiums and co-payments. AT&T says it wants employees to shoulder more of their growing health care costs.