DENVER (AP) — CenturyLink and the union representing 13,000 workers in 13 states in the West and Midwest have failed to reach a contract agreement, but have signed onto a day-to-day extension of the expired pact.The Communications Workers of America made the announcement after the existing labor contract expired at 11:59 p.m. Saturday. CWA spokesman Al Kogler said in a statement that negotiations will continue and workers will remain on the job during the extension.Kogler has said the union opposes a proposed increase in health care premiums and wants to bring more jobs back to the U.S. The union had authorized a strike in the event that a new deal couldn't be reached with the Monroe, La.-based telecommunications company.CenturyLink workers in Montana, who are negotiating a separate contract, also agreed to the extension.