'Put mayonnaise on it, you'll be good." This is what Martisse Campbell, who works at McDonald's in Philadelphia, said her manager told her co-worker when she was badly burned on the job.

More than two dozen other workers in 18 cities across the country filed similar health and safety complaints against the fast-food giant on March 16, claiming that understaffing and pressure to work too quickly has led to burns, falls and other serious injuries. They allege that many McDonald's stores lack proper medical supplies to treat injuries incurred on the job, and that workers are often told to treat burns with condiments such as mustard rather than burn cream.

The 28 complaints were filed with the federal Occupational Safety and Health Administration and came at the same time that a national survey of fast-food workers found that four in five employees have been burned on the job. The poll - conducted via Facebook, by Hart Research Associates, a company that often polls for labor groups - claims that of the 1,426 fast-food workers surveyed, 87 percent reported having at least one injury in the past year.

"Incredibly, one-third of all burn victims say that their manager suggested wholly inappropriate treatments for burns, including condiments such as mustard, mayonnaise, butter or ketchup, instead of burn cream," the firm states.

Such is the case with Brittney Berry, a Chicago worker who claims that she was under so much pressure to work quickly that she slipped and caught her arm on the grill, leading to a serious burn that caused nerve damage.

"The managers told me to put mustard on it, but I ended up having to get rushed to the hospital in an ambulance. This is exactly why workers at McDonald's need union rights," she said in a statement released by the National Council for Occupational Safety and Health.