Thousands of downtown Chicago hotel workers went on strike Sept. 7 after contracts expired at 26 downtown convention and boutique hotels. Unite Here Local 1, the union for housekeepers, servers, cooks and doormen, had warned of a possible walkout when the previous contracts expired on August 31. At some properties, popular restaurants were forced to cease operations, as well.

More: Hospitality Strike Votes Could Increase with Arrival of High-Tech Hotels, Minimum Wage Increases

The union represents more than 15,000 hospitality workers across the Chicago area, and more than 6,000 workers are covered by the expired contracts.

A union spokesperson cited lack of year-round health benefits for full-time workers as a major sticking points in contract negotiations. Protection against sexual harassment and other assaults was another issue on the table. In a separate development, Marriott International announced it is ramping up deployment of alert devices for housekeepers and other on-property employees, enabling them to discretely summon help if they feel harassed or spot a guest in distress.

Properties affected by the strike include Hyatt Regency Chicago, JW Marriott Chicago, Sheraton Grand Chicago and Hilton Chicago Michigan Avenue. A complete list can be accessed at Around-the-clock picket lines will begin at the targeted properties, the union announced.

Paul Ades, senior vice president for labor relations at Palmer House Hilton, told Chicago Tribune that the strike will have “minimal impact” on operations. A statement by Marriott International, which operates six affected hotels, said, “The parties are not at an impasse on any issue.” Each hotel company negotiates separately with the union.

The move comes less than four months after culinary and bartenders’ unions for casinos in Las Vegas narrowly averted a similar walkout. You can read more about trends playing a role in contract negotiations here.