About 7,700 employees of Marriott International, the world’s largest hotel chain, are now walking picket lines in Boston, Detroit, Oakland, San Diego, San Francisco and San Jose, as well as two cities in Hawaii.

Nearly 2,500 Marriott hotel workers at seven downtown San Francisco properties walked off their jobs Thursday morning, threatening to disrupt the city’s busy fall convention season.

According to San Francisco Chronicle, several dozen picketers marched outside The Westin St. Francis San Francisco on Union Square chanting, “No contract? No peace” and carrying signs that read, “One job should be enough.”

Moscone Center is currently the site of IDWeek, a health care conference. Upcoming this month are Anesthesiology 2018 (Oct. 13–17) and Oracle’s OpenWorld (Oct. 22–25), one of the year’s largest meetings in the city.

Marriott said it was “disappointed” by the decision of Unite Here Local 2 to strike now. “During the strike our hotels are open,” the company said in a statement, “and we stand ready to provide excellent service to our guests. While we respect our associates’ rights to participate in this work stoppage, we also will welcome any associate who chooses to continue to work.”

Anand Singh, president of Unite Here Local 2, said in a statement, “We’re going to stay on the picket line until Marriott workers no longer need to work two or even three full-time jobs just to make ends meet.”

In Chicago, workers at nine downtown hotels representing several major hotel brands remain on strike. Workers at other brands in that city, including Marriott, have agreed to a new contract that reportedly includes health-care coverage in the winter—when many workers are temporarily laid off—for the first time.

Major issues in all affected cities include wages, health care, the threat of technology eliminating jobs and protection from harassment from guests.

Last month, Marriott said it was giving housekeepers and other workers an alert device to summon help if they feel threatened or need help.

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