Kaiser Permanente workers will begin voting Monday on whether to authorize a massive strike that would affect Kaiser facilities nationwide, according to the Service Employees International Union, one of the unions representing Kaiser workers.

Workers at Kaiser Permanente Medical Center in Oakland will vote on Monday. Voting will go on for more than a month as Kaiser workers in California, Oregon, Washington, Colorado, Virginia and Washington, D.C. cast ballots.

If authorized, the strike will begin in early October. If approved, the union said it would be the biggest strike in 20 years. According to the union, Kaiser workers have been without a contract since Sept. 30 and talks stalled on July 12.

The union is accusing Kaiser of unfair labor practices, saying that the healthcare company is paying its executives exorbitant salaries while not providing adequate resources to workers and patients.

A spokesperson for Kaiser did not immediately return a request for comment.