The labor contracts of 50,000 workers at Las Vegas' Strip and downtown casinos expired at midnight Thursday, raising the prospect of a strike.

They include bartenders, food and cocktail servers, porters and cooks at 34 casino resorts who are members of the Culinary Union. By 4:30 a.m. ET on Friday, the union had not called for an actual walkout.

Last week, 25,000 unionized workers voted 99 percent in favor of authorizing a strike should their contracts expire.

Caesars Entertainment Corporation and MGM Resorts International — as well as other properties including Caesars Palace, the Bellagio, the MGM Grand, Excalibur and Luxor — are all potentially affected.

1am update: Contract negotiations ongoing with @CaesarsEnt. No deal has been reached. The Culinary Union has *not* yet called for a strike walkout.



🚨Friday, June 1: Strike HQ opens at 10am. pic.twitter.com/amI3lXUibV — The Culinary Union (@Culinary226) June 1, 2018

If a large-scale strike is called, it would be the first in more than three decades.

The Culinary Union said in a statement early Friday that hospitality workers were now "preparing for a citywide strike" and planned to begin making "thousands of strike picket signs."

The union added that negotiations were ongoing with Caesars Entertainment regarding a new contract.

On Thursday, union spokeswoman Bethany Khan said no more meetings had been scheduled with MGM.

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

Caesars Entertainment issued a similar statement saying 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."

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.

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, documents released by the union say.

Around 24,000 workers are affected under the MGM contract and 12,000 are under the Caesars contract, the union said.

The average hourly wage of Las Vegas Strip workers is $23, including benefits such as premium-free health care, a pension and a 401(k) retirement savings plan, and $20,000 down-payment assistance for first-time homebuyers.

Downtown casino and resort properties could be affected as well. The union says the expiring contracts affect workers at the Golden Nugget, the D, Binion’s and El Cortez, among others.

The last time there was a city-wide strike involving casino workers was in 1984. That strike spanned 67 days. During that time, union members lost an estimated $75 million in wages and benefits, while the city lost a similar amount in tourism revenue, the Associated Press reported. Millions more were lost in gambling income.

The Culinary Union released an analysis from UNITE HERE Gaming Research on Wednesday that estimated a one-month strike could cost MGM Resorts International and Caesars Entertainment Corporation over $300 million in operating profits.

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

In Clark County, where Las Vegas is located, gaming revenue was around $9.5 billion in fiscal year 2017, with more than $6 billion of that coming from the Las Vegas Strip, according to a Nevada Gaming Control Board report released in January (those numbers are before expenses are taken into account).

And the Las Vegas Golden Knights hockey team, which are in the Stanley Cup playoffs in their first year, have home games scheduled in Las Vegas against the Washington Capitals beginning June 7, adding to the potential loss in tourist and casino revenue.

The union has called on visitors to not patronize hotels and casinos if a strike is called, and are urging people not to cross picket lines if there is a labor action.