Workers at McDonald’s say their jobs burn—literally. Now the Occupational Safety and Health Administration may investigate those injuries, which, while not uncommon in working kitchens, were allegedly treated in a manner befitting the Franco-Prussian War.

In the late 1800s, Prussian Surgeon General Friedrich Von Esmarch—widely believed to be the first person to conceive of first aid treatment—recommended that burns suffered on the battlefield be coated with cooking oil, animal fat, or butter. As historical burn treatments go, that’s a rather tame prescription, really. An ancient Egyptian treatment from 1500 B.C., one of the oldest ever found, calls for changing salves depending on how fresh the injury is, moving from, say, frogs cooked in oil to fermented goat dung.

While both butter and frog oil run contrary to modern medicine, only one has allegedly been recommended to treat workplace injuries in lieu of burn cream at McDonald’s restaurants.

On Monday, a group of workers filed 28 work-safety-violation claims against McDonald’s and franchise owners in 19 cities with OSHA and state authorities. According to a survey conducted by Hart Research Associates, also published on Monday, 79 percent of fast-food workers have suffered burns at work—and one-third say they were told to treat the injuries using butter or condiments such as mustard or ketchup as a salve.

“My managers kept pushing me to work faster, and while trying to meet their demands I slipped on a wet floor, catching my arm on a hot grill,” Brittney Berry, who has worked at a Chicago McDonald’s since 2011, said in a statement. “The managers told me to put mustard on it, but I ended up having to get rushed to the hospital in an ambulance.” The accident left her with nerve damage, according to a press release.

According to the Hart Research survey, which included responses from 1,426 fast-food workers, 29 percent say understaffing contributed to the circumstances that led to their injuries.

The group Fight for $15, which, with assistance from the Service Employees International Union, has organized wage protests for fast-food workers, compiled the stories of a number of injured workers in a new video. (The group also helped workers file the OSHA complaints.) In several instances, the employees said there weren’t adequate first-aid materials, and that they were told to treat burn injuries with ketchup or mustard.

“McDonald’s and its independent franchisees are committed to providing safe working conditions for employees in the 14,000 McDonald’s Brand U.S. restaurants. We will review these allegations,” Heidi Barker Sa Shekhem, a McDonald’s spokesperson, said in an emailed statement. “It is important to note that these complaints are part of a larger strategy orchestrated by activists targeting our brand and designed to generate media coverage.”

The workplace-safety complaints are the latest in a string of legal challenges that have come to represent a second front in the ongoing battle over wages between workers and fast-food employers. In January, Fight for $15 helped file a federal civil rights lawsuit against McDonald’s, alleging both racist and sexist treatment of employees. The group was also involved in the complaints filed with the National Labor Relations Board that led to the landmark ruling that McDonald’s is considered a joint employer along with franchise owners. Last year also saw lawsuits alleging wage theft and other pay-related abuses filed in California, Michigan, and New York, although without involvement from Fight for $15.

After being burned on the job, Brittney Berry told reporters on a Monday conference call that she was unable to work for three weeks and had to go without pay for that period.