McDonald’s Corp. restaurant workers from 19 U.S. cities complained to regulators on Monday that their working conditions are hazardous and have led to severe burns from hot grills and fryer oil.

Workers taking part in the Service Employees International Union-backed “Fight for $15” an hour campaign opened a new front in their two-year drive to increase pay and improve conditions in the fast-food industry by filing 28 state and federal complaints over health and safety.

McDonald’s workers, who already have claimed that they have been subjected to wage theft, racial discrimination and retaliation for attempting to unionize, hope to hold McDonald’s Corp. responsible for the actions of its franchisees.

Some experts say a win could force the company to negotiate with workers and the union.

The latest complaints, targeting 19 franchised restaurants and nine operated by McDonald’s Corp. in cities such as New York, New Orleans and Philadelphia, were filed over the last two weeks with the U.S. Occupational Safety and Health Administration (OSHA) and state authorities. Other cities include Kansas City, Mo., and Miramar, Fla.

They said workers were pressured to clean and filter fryer oil while it was still hot. They also said that many stores lacked basic first aid kits or protective gear and that managers told workers to treat burns with condiments such as mustard and mayonnaise.

McDonald’s said the company and its franchisees are committed to providing safe working conditions for employees in the brand’s roughly 14,000 U.S. restaurants.

“We will review these allegations,” Heidi Barker Sa Shekhem, a spokeswoman, said in a statement.

Brittney Berry, 24, said she was rushing to meet managers’ demands to work faster when she slipped and fell on a wet floor at a McDonald’s restaurant in Chicago, suffering a severe grill burn on her forearm and nerve damage to her wrist.

“The managers told me to put mustard on it, but I ended up having to get rushed to the hospital in an ambulance,” said Berry, who still works at the restaurant where she was injured.

“Fight for $15” organizers say McDonald’s Corp. and its franchisees should be considered “joint employers” because the corporation wields significant control over operations at franchised restaurants with things like technology and compliance programs.

John Tomich, a safety consultant and former OSHA area director for New York, said it would be “legally challenging” to make that case in this context.