(Reuters) - A union-backed group said it had filed complaints on behalf of 15 U.S. McDonald’s workers who say they were sexually harassed on the job, in the latest challenge to how the fast-food company and its franchisees treat employees.

The logo of Dow Jones Industrial Average stock market index listed company McDonald's (MCD) is seen in Los Angeles, California, U.S. on April 22, 2016. REUTERS/Lucy Nicholson/File Photo

Fight for $15, which has organized strikes and protests calling for employers to raise wages, said on Wednesday that it filed the administrative complaints with the U.S. Equal Employment Opportunity Commission against McDonald’s USA LLC and individual franchisees in eight states over the last month.

Cycei Monae, a McDonald’s worker in Flint, Michigan, said a manager showed her a picture of his genitals and said he wanted to “do things” to her, according to a complaint provided by Fight for $15. Corporate officials ignored her complaints, Monae said on a phone call with reporters on Wednesday.

In another complaint, a worker in Folsom, California, said a supervisor offered her $1,000 for oral sex.

Thirteen of the complaints were by women, and two were by men, said Fight for $15, which the Service Employees International Union formed in 2012.

“As the country’s second-largest employer, McDonald’s has a responsibility to set standards in both the fast-food industry and the economy overall,” Kendall Fells, organizing director for Fight for $15, said in a statement.

McDonald’s spokeswoman Terri Hickey said the company takes harassment complaints seriously and was reviewing the allegations.

“At McDonald’s, we and our independent owner-operators share a deep commitment to the respectful treatment of everyone,” she said in a statement.

The EEOC, a federal agency that enforces discrimination laws, does not comment on complaints it receives, it said. It can file lawsuits on workers’ behalf or grant them permission to bring their own cases.

While most of the complaints were filed on behalf of employees at franchised restaurants that McDonald’s Corp does not own, all of them say the company is responsible for the harassment because it controls working conditions there.

McDonald’s is also facing a class-action lawsuit in federal court in San Francisco by 800 workers at several franchised restaurants who say they are owed overtime pay and were forced to skip breaks.

The company has denied that it is a “joint employer,” a designation that could render it liable for labor law violations by franchisees and require it to bargain with workers at those restaurants if they unionize.

In a case before the National Labor Relations Board, Fight for $15 claims the company is a joint employer of franchise workers who say they faced retaliation for joining in nationwide strikes organized by the group. McDonald’s has said it neither retaliated against workers at its own restaurants nor instructed franchisees to do so.