Fast-food workers in more than 100 cities plan to walk off the job Thursday. The goal is a higher wage: $15 an hour. The Service Employees International Union, the SEIU, is backing the workers.

“They are not giving up until they are heard, and $15 and a union becomes a standard of practice in all fast-food restaurants in the United States,” says Mary Kay Henry, the union’s president. Corporations argue that would be bad for business.

The SEIU has spent millions of dollars getting the word out, but it has also asked home-care workers, a group it recently unionized, to strike in solidarity with the fast-food workers.

“I think it is part of the redefinition of what a union really is and how unions operate,” says Thomas Kochan, a professor at the MIT Sloan School of Management.

According to Ruth Milkman, a sociologist at The Graduate Center, CUNY, this push for a higher minimum wage is part of “a comprehensive campaign with lots of different pieces” born out of necessity.

“The traditional approach to unionization that SEIU and other unions have used isn’t really working too well these days, and they recognize that, and they are interested in experimenting with new approaches and new methods,” she says, noting that less than 7 percent of private-sector employees are unionized.

The real question, argues Harry Holzer, a labor economist at Georgetown University, is: “Is there really pressure on employers to raise wages?” Sure, a daylong strike affects the bottom line, but, he points out, that is nothing compared to what it would cost them to raise wages and offer better benefits.