Members of the Unite Here Local 2 began a rally outside the hotel at Third and Howard streets at about 6 a.m. They plan to continue the two-day informational picket until 10 p.m. Thursday, union officials said.
The workers are protesting proposed cuts to health and retirement benefits.
"There has never been a question of whether they can afford what's on the table," Mike Casey, president of Local 2, said in a statement. "The question is whether these companies will make a business decision that's in the best interests of the workers, the city and the hotels themselves."
A spokesman for the Hotel Council of San Francisco released a statement Tuesday in anticipation of the protest, saying that instead of "laying siege" to a hotel that contributes to the city's tourism industry, union members should focus on the bargaining process.
"Unions and businesses need to work together to preserve important industries with large numbers of employees," spokesman Sam Singer said.
"The demise of the American automobile industry shows the folly of unreasonable and unsustainable union demands," he said.
Last month, hotel workers carried out separate three-day strikes at the Grand Hyatt, the Palace Hotel and the Westin St. Francis.