Fast-food workers across the United States are expected to stage their largest strike to date on Thursday in an almost year-long campaign to raise wages in the service sector.

Employees of McDonald's Corp, Wendy's Restaurants, Burger King Worldwide and others have pledged to walk off their jobs in 50 cities from Boston, Massachusetts, to Alameda, California, organisers say. They are expected to be joined by retail employees at stores owned by Macy's, Sears Holdings Corp and Dollar Tree in some cities.

The strike follows a similar protest last November, when some 200 workers walked off their fast-food jobs in New York City. Groups in Chicago, Kansas City, Detroit and other cities followed their lead in April and July.

The workers are demanding that the federal minimum wage be raised to $15 per hour from the current $7.25. They also want to form unions without facing retaliation from franchisees or their parent companies.

The median wage for front-line fast-food workers is $8.94 per hour, according to an analysis of government data by the National Employment Law Project, an advocacy group for lower-wage workers. Virtually all private-sector fast-food jobs are non-union, and organisers say retaliation against workers who try to organise is common.

Martin Rafanan, a community organiser in St Louis, Missouri, where the minimum wage is $7.35, said local employees of McDonald's and Wendy's were inspired by the Occupy Wall Street movement's discussions about income inequality. But he added that the main reason for their frustration is financial.

"If you're paying $7.35 an hour and employing someone for 20, 25 hours a week, which is the average here, they're bringing home about $10,000 a year. You can't survive on that." Rafanan said.

"Unless we can figure out how to make highly profitable companies pay a fair wage to their workers, we're just going to watch them pull all the blood, sweat, tears and money out of our communities."

The National Restaurant Association, the trade group for US restaurants and fast-food chains, said in a statement that the restaurant industry provides 13 million Americans with jobs and that discussions about wages "should be based on facts."

"Only five per cent of restaurant employees earn the minimum wage and those that do are predominantly working part-time and half are teenagers," said Scott DeFife, the organisation's executive vice president of policy and government affairs.

Fast-food companies, which have not altered wage policies as a result of recent strikes, have struck a similar tone. Many of them have said they provide good jobs and ample opportunities for workers looking to rise through the ranks.

"McDonald's aims to offer competitive pay and benefits to our employees. Our history is full of examples of individuals who worked their first job with McDonald's and went on to successful careers both within and outside of McDonald's," the company said in a statement.

Wendy's and Burger King did not respond to requests for comment.

Thursday's strike is shaping up to be "the largest attempt at worker organising in this industry ever" thanks to broad financial and technical support from the Service Workers International Union, and grassroots efforts from community groups, local politicians and the clergy, said Tsedeye Gebreselassie, an attorney at the National Employment Law Project.

"The workers are responding to total failure on behalf of the federal government to raise the minimum wage to keep up with inflation and the cost of living," Gebreselassie said.

The $200 billion US fast-food sector has come under the spotlight because lower-paying and part-time service work, including retail sales and food preparation, has made up most of the jobs added since the recession.

The pre-Labour Day strikes will include movements in several Southern states, a region that has historically been challenging for organised labour.

Dorian Warren, an assistant professor of political science at Columbia University who has published work on labour organising and inequality, said that, while the movement is still in its early stages, the significance of protests in states such as Mississippi, Louisiana and Alabama is "a huge, huge deal."

"The South has always been the model for low wage employment, from slavery to the Jim Crow laws, to the present. It's also the most anti-union part of the country, so the fact that workers feel empowered enough to take collective action is enormous," Warren added. - Reuters