Employees and supporters demonstrate outside of a Wendy's fast-food restaurant to demand higher pay and the right to form a union on July 29, 2013 in New York City. - 

You may have to wait longer for your Egg McMuffin or iced coffee this morning. Thousands of fast-food workers in about 35 cities are planning to strike, as their call for higher pay, which started in New York last fall, goes nationwide.

Workers at McDonald’s, Popeye’s, Taco Bell and other fast-food chains are demanding $15 an hour -- twice as much as many now earn.

"The strike among fast food workers is a very strange type of strike," says Gary Chaison, a professor of labor relations at Clark University.

He says that's because it cuts across many companies and employers, meaning the franchisees who own the bulk of fast-food restaurants. The strike is being bankrolled by the Service Employees International Union, or SEIU, at the cost of millions of dollars. SEIU President Mary Kay Henry says even though the workers aren't dues-paying members, supporting them is a good investment for the union.

"These workers need to make a living wage," she says. "At the SEIU, we believe in improving conditions for all workers."

"This is a very smart idea for the unions," agrees Harley Shaiken, a labor professor at the University of California, Berkeley. "Unions are going back to their roots. They’re speaking for the dispossessed, the most vulnerable."

Shaiken says that idealism is great for the union’s image. But will the strikes work for the workers? Chaison doesn’t think so.

"The times may not be right for increasing wages, particularly if it’s seen as possibly jeopardizing jobs," he says.

Workers risk being fired if they walk off the job during a shift, so many join the picket line on their day off. Though the protests have gained momentum and scope, just a tiny fraction of fast-food workers is taking part.

Follow Stacey Vanek Smith at @svaneksmith