Mayor Gavin Newsom also is now getting involved in the negotiations.
More than 300 Grand Hyatt workers with the union Unite Here Local 2 have been picketing since Thursday morning outside the hotel, located at 345 Stockton St., according to union spokesman Ian Lewis.
Union officials have said hotel management is proposing unreasonable reductions in health and retirement benefits.
Newsom was working on the issue this afternoon and has asked for the employees and management to sit down with him for a meeting that will likely take place early next week, according to Nathan Ballard, a spokesman for the mayor.
The union represents about 12,000 employees in the hospitality industry in San Francisco and on the Peninsula, including room cleaners, cooks, food servers, bellmen, bartenders and dishwashers.
Lewis said a steady drizzle that has fallen in San Francisco today has not stopped large numbers of employees from joining the picket lines. "There's still a number of folks on the line, even in the rain, and everyone's in great spirits," he said.
The workers will return to work Sunday morning, but are calling on customers to honor an ongoing boycott of the hotel. Union workers at other San Francisco hotels remain on the job, but job actions elsewhere still remain a possibility.
Negotiations have been going on for more than two months, and workers have been without a contract since Aug. 14.
The union is negotiating separately with each of the 31 hotels where its members work, including those owned by Hyatt, Hilton, Marriott, Starwood and Intercontinental.
Officials with the Grand Hyatt San Francisco released a statement Thursday about the strike.
"We are disappointed with the action taken ... by Local 2. After only five bargaining sessions the union has decided to engage in disruptive and counterproductive action instead of trying to achieve progress at the negotiating table," hotel management said.
"It is not in anyone's best interest to try to damage the hotel guest experience, disrupt our associates and purposefully do economic harm to the city of San Francisco," the statement read.
Along with the strike, union officials today were also planning a 4:30 p.m. rally outside the hotel and invited union members from the 30 other local hotels to join the protest.
Riddhi Mehta, a spokeswoman for the union, said as many as 500 people could show up at the rally.