Some workers claimed they had been told to treat their injuries with condiments such as mustard and mayonnaise rather than medicinal cream.
A McDonald’s spokeswoman said the firm would review the allegations.
The company could face fines of up to $70,000 (£47,000) for each violation.
The complaints by McDonald’s employees were filed in the past few weeks to the US Occupational Safety and Health Administration (OSHA) and publicised by the Fight for $15 group, which campaigns for better wages and conditions for fast food workers.
A OSHA spokesman confirmed that the agency had opened investigations as a result of the complaints.
He added that McDonald’s could face fines of between $7,000 and $70,000 for each safety infraction, depending on the severity.
In response to the allegations, McDonald’s spokeswoman Heidi Barker Sa Shekhem said the company and its independent franchisees were “committed to providing safe working conditions for employees in the 14,000 McDonald’s Brand US restaurants”.
A seperate survey of 1,426 fast-food workers, carried out on behalf of the US National Council for Occupational Safety and Health, found that almost 80% had suffered burns in the past year.
One third of the burn victims said their manager suggested they treat their injuries with condiments such as mustard, mayonnaise, butter, or ketchup.