Headed into the busiest weekend of its year, Atlantic City remains under threat of a strike that could see picket lines at five of the New Jersey city’s eight casinos.

Unless a deal is reached by Friday, as many as 6,500 cooks, cleaners, cocktail servers and other workers could walk off their jobs at Bally’s Atlantic City Hotel and Casino, Harrah’s Resort Atlantic City, Caesars Atlantic City Hotel and Casino, the Trump Taj Mahal and the Tropicana, according to Bob McDevitt, president of Unite Here Local 54.

Workers are looking for raises on pay that averages less than $12 an hour. Casinos that survived the downturn in business at the seaside city are thriving, he said, and workers want to share in the rebound.

“As we get closer to the deadline I think the industry will be more and more concerned about the reality of a strike,” Mr. McDevitt said.

With the strike deadline looming, talks aimed at a new contract are taking place through the week, he said.

Bally’s, Harrah’s and Caesars are owned by Caesars Entertainment Corp., which is owned by Apollo Global Management and TPG. A separate Caesars business, the company’s main operating unit, is operating under chapter 11 protection in Chicago.

Caesars Entertainment couldn’t be reached Tuesday to discuss the threat of a strike. In a June 16 statement in response to inquiries about the strike authorization vote, Caesars Entertainment spokeswoman Katie Dougherty said: “Our goal remains to negotiate a fair resolution to keep our employees at work for their sake and to continue supporting Atlantic City’s revitalization which has our full commitment.”

Billionaire Carl Icahn’s company, Icahn Enterprises LP, owns the Tropicana and Trump Taj Mahal. He couldn’t be reached for comment.

Three casinos—Borgata Hotel Casino and Spa, Resorts Casino Hotel and Golden Nugget Atlantic City—aren’t under threat of a strike, Mr. McDevitt said. Their owners “are not committed to destroying middle-class jobs in Atlantic City,” he said.

The aging gambling hub has turned into a battleground for politicians and labor leaders who contend business interests haven’t held up their end of the bargain struck when Atlantic City opened the door to casinos.

Thousands of jobs have evaporated, and people who have worked for years at casinos “can’t afford to pay their rent, can’t afford to feed their kids and can’t afford to live above the poverty level,” Mr. McDevitt said.

Some 96% of the roughly 3,000 workers who turned out for a strike vote authorized a work stoppage unless there is progress at the bargaining table, according to the union. Workers at the Trump Taj Mahal, who lost their health-care benefits in the casino’s most recent bankruptcy, voted earlier for a strike.

Once the workers turned out in force, the atmosphere at the bargaining table “changed dramatically,” Mr. McDevitt said. “They seem to want to get to a deal, but, as always, the devil’s in the detail and the deal that they want may not be a deal the workers would accept.”

Write to Peg Brickley at This e-mail address is being protected from spambots. You need JavaScript enabled to view it