CHICAGO – The National Labor Relations Board on Friday issued 13 complaints against McDonald's and some of its franchisees, calling them joint employers and alleging they violated labor rights of employees at various restaurants nationwide.

The labor board found merit in 86 cases filed in cities from New York to Chicago to San Francisco. The cases allege that Oak Brook, Ill.-based McDonald's and its franchisees retaliated against employees for engaging in activities, including nationwide protests calling for higher wages and better conditions.

Retaliation included threats, surveillance, reduction of hours, interrogations and firings, the board said.

The ruling, which McDonald's vowed to appeal, is significant because it could increase the fast-food giant's responsibility in labor cases and, potentially, that of other types of employers as well.

"It's a game-changing decision," said Robert Bruno, a professor of labor and employment relations at the University of Illinois at Chicago.

Bruno said the decision shatters the wall that has kept franchisees and franchisers separate. For years, labor groups have complained the wall keeps major corporations from taking direct responsibility for their employees.

McDonald's has long maintained that its franchisees are independent owner-operators who set their own policies, including wages, while adhering to corporate standards in areas such as food preparation and restaurant design.

But the board said its investigation found that McDonald's "engages in sufficient control over its franchisees' operations, beyond protection of the brand."

In a statement, McDonald's said it is disappointed with the board's decision and will contest the joint-employer designation and the unfair labor practice charges.

"The National Labor Relations Board's actions today improperly and dramatically strike at the heart of the franchise system — a system that creates economic opportunity, jobs and income for thousands of business owners and their employees across the country.

"This relationship does not establish a joint employer relationship under the law — and decades of case law support that principle," the company said.

Business groups said the NLRB's decision brings uncertainty to business owners and investors because it could affect a range of employers beyond McDonald's, such as other companies with franchise models.

"This is the nightmare before Christmas," said Robert Cresanti, executive vice president of government relations and public policy at the International Franchise Association. "It is a devastating blow to this industry."