The stakes just got raised in a contract clash between unionized casino workers and their employers.

The two biggest resort operators in Las Vegas could lose over $10 million a day combined starting at midnight on Thursday if an approved strike goes through, according to the union representing some of the staff.

The Culinary Union released estimates of what would happen at MGM Resorts International and Caesars Entertainment, which run more than half the properties that would be affected if the more than 50,000 employees went on strike.

Volunteer Jenifer Murias yells into a megaphone as Culinary Union members file into a university arena to vote on whether to authorize a strike on May 22 in Las Vegas. Isaac Brekken / AP file

“It is difficult to gauge the potential impact of a large-scale strike in Las Vegas since we haven’t had one since 1984, but we think a strike now would significantly impact MGM and Caesars’ operations on the Strip,” said Ken Liu, an analyst for the union, in a statement.

The stalemate could cut into casino profits and leave them shorthanded, the union said on Wednesday.

"One might assume a 10 percent worsening of operating margins due to the use of less experienced and less skilled replacements...to keep the doors open, rooms cleaned, food cooked, and cocktails served, not to mention other factors such as the disruptions to management staff’s regular work,” the union wrote.

If the strike were to last a month, losses for the casinos could be upwards of $315 million, said Liu.

The union has failed to come to terms with management over a new contract, citing grievances like wages, training, sexual harassment by guests, and the fear of various positions being replaced by robots or automation.

The union says they've asked MGM and Caesars for annual raises of about 4 percent for the next five years while the casinos have countered with 2.7 to 2.8 percent, a document released by the union says.

Casino employees are increasingly concerned about the encroachment of technology into the workplace. Some have lost jobs to new electronic reservation and room service systems.

Workers are fighting for new contracts that provide a greater measure of security for members including workplace safety, sexual harassment, subcontracting, technology, and immigration. In an event of a strike, please do not cross picket lines. pic.twitter.com/oRBMp693u0 — The Culinary Union (@Culinary226) May 31, 2018

Chad Neanover, a prep cook at Margaritaville, a Caesars property, was quoted by the union as saying he voted to strike "to ensure my job isn't outsourced to a robot."

The Culinary Union includes many of the support staff who keep a casino running, from bartenders to servers to kitchen workers, but doesn't cover dealers. Casino-resorts not affected by the strike include Wynn Las Vegas, Encore, the Venetian, and the Palazzo.

Caesars said in a statement Thursday that it "continues to meet with the Culinary Union to finalize a new 5-year contract," and "we are confident that we will achieve a tentative agreement without a work stoppage."

MGM Resorts International said in a statement on Thursday that "We are confident that we can resolve the outstanding contract issues and come to an agreement that works for all sides."