Costco‘s unionized workers voted to strike if they fail to agree to a contract by Jan. 31.

The strike would affect more than 600 locations nationwide. A group of about 18,000 unionized workers voted in favor of the move in order to negotiate pay increases, more retirement benefits, updated bereavement policies, and provisions for holidays and inclement weather.

Teamsters negotiators have been in talks with Costco for almost a month. Both came to an agreement about seniority rights and the shop stewards’ roles, among other things, but have clashed on these economic issues. The final negotiation is slated for Monday.

“Our members have spoken loud and clear — Costco must deliver a fair contract, or they’ll be held accountable,” Teamsters General President Sean M. O’Brien said in a statement. “Costco’s greedy executives have less than two weeks to do the right thing. If they refuse, they’ll have no one to blame but themselves when our members go on strike.”

Costco closes for a few holidays, including New Year’s Day, Easter Sunday, Memorial Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day.

The Washington Examiner reached out to Costco for comment.

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Practice pickets went on at various locations last week. Hayward, California; Sumner, Washington; and Long Island, New York, locations saw their employees stand outside with signs.

The next shareholders’ meeting will be held after the last scheduled negotiations on Wednesday.