More than half of fast-food workers’ families receive some sort of public assistance, costing the nation $7 billion a year, according to a new report distributed by a group that has been pushing for union representation and higher wages for fast-food workers.

Fast-food workers earn an average of $8.69 an hour, and often work fewer than 40 hours a week, qualifying them for food stamps, Medicaid and tax credits, according to the report, written by economists at the University of California-Berkeley and the University of Illinois at Urbana-Champaign.

Even before it was released publicly, the report raised the ire of some conservative groups that said it used faulty methodology to prove a point.

“In its quest to unionize the fast-food industry, the (Service Employees International Union) has demonstrated that it will leave no stone unturned — including using ‘research’ and arguments that would get a higher grade in creative writing than in a high-school economics class,” said Michael Saltsman, research director at conservative think tank Employment Policies Institute, in a statement.

The report calculates that about $3.9 billion a year is spent on Medicaid and children’s health care for fast-food workers and their families. Families also receive $1.04 billion in food stamp benefits and $1.91 billion from the federal government through the earned income tax credit.

McDonald’s, which has 707,850 employees, costs $1.2 billion in aid, the report said; Yum Brands, which includes Pizza Hut, Taco Bell and KFC, and employs 379,449, costs $648 million.