A Las Vegas casino workers union that has threatened a citywide strike said Friday that it had reached a tentative deal with a major Las Vegas Strip company that could cover around a quarter of the 50,000 workers affected in labor negotiations.

The Culinary Workers Union said it agreed with Caesars Entertainment on what it called a "historic" five-year deal that covers approximately 12,000 workers. A vote to ratify the contract has not been set yet.

Labor contracts with casino resort operators on the Las Vegas Strip and downtown Las Vegas affecting around 50,000 workers expired at midnight Thursday, the union said.

Last week, 99 percent of around 25,000 union workers voted to authorize a strike, but no strike has been called yet.

Details of the tentative agreement with Caesars were not immediately released. Union spokeswoman Bethany Khan said in an email Friday that the tentative deal with Caesars is for nine properties on the strip: Bally's, Flamingo, Harrah's, Paris, Planet Hollywood, the Cromwell, the Linq, Caesars Palace and the Rio.

The other major Strip operator is MGM Resorts International. No deal with the union and MGM has been reached, Khan said, and negotiations and strike preparations were continuing Friday. The expired contracts at MGM properties affect around 24,000 workers.

MGM said in a statement Friday that it is scheduling more negotiations. “We’ve made good progress in resolving the remaining issues, and we will continue to negotiate to allow these productive talks to continue," the company said.

"We remain dedicated to negotiating a contract that demonstrates our commitment to employees and their families while our company continues creating good jobs and future opportunities in Las Vegas," MGM Resorts International said. "We remain confident that we will reach an agreement."

During negotiations after the last contract with MGM expired in 2013, negotiations went on for months before a deal was reached in November of that year.

Culinary Workers Union Local 226 represents bartenders, food and cocktail servers, porters and cooks. The union said last week that 34 properties, mostly on the Las Vegas Strip, were affected by the expiring labor contracts.

The union said on Twitter Friday that preparations were being made for a possible large-scale strike.

The union has failed to come to terms with management over a new contract, citing grievances over wages, training, sexual harassment by guests and automation.

The union said in documents released this week that it has 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 citywide strike of casino and resort workers would be the first in Las Vegas since 1984.

That labor action lasted 67 days and is estimated to have cost the the Culinary Workers Union $75 million in wages and benefits, while the city lost a similar amount in tourism and gambling revenue, the Associated Press reported.

Around 42 million people visited Las Vegas in 2017, according to the Las Vegas Convention and Visitors Authority. The authority says spending sourced to those 42 million visitors that year was estimated at $34.8 billion.