New York --

Fast-food workers in about 100 cities will walk off the job Thursday, organizers say, which would mark the largest effort yet in their push for higher pay.

The actions are intended to build on a campaign that began about a year ago to call attention to the difficulties of living on the federal minimum wage of $7.25 an hour, or about $15,000 a year.

The protests are part of a movement by labor unions, Democrats and other worker advocacy groups to raise pay in low-wage sectors. Last month, President Obama said he would back a Senate measure to raise the federal minimum wage to $10.10.

Protesters are calling for $15 an hour, although many see the figure as a rallying point rather than a near-term possibility.

It's not clear how large the turnout will be at any given location, or whether the walkouts will be enough to disrupt operations. Similar actions this summer had varying results, with some restaurants unable to serve customers and others seemingly unaffected.

The National Restaurant Association, an industry lobbying group, called the demonstrations a "campaign engineered by national labor groups," and said the vast majority of participants were union protesters rather than workers.

The group added that past demonstrations "have fallen well short of their purported numbers."

Kendall Fells, an organizer for Fast Food Forward, said demonstrations are planned for 100 cities, in addition to the 100 cities where workers will strike. He said plans started coming together shortly after the one-day actions in about 60 cities this summer.

"They understand they're not going to win from a one-day strike," Fells said of workers.

Still, organizers face an uphill battle in reshaping an industry that competes aggressively on low prices, a practice that has intensified as companies including McDonald's Corp., Burger King Worldwide Inc. and Yum Brands Inc. face growing competition and slow growth in the weak economy.

Fast-food workers are also seen as difficult to unionize, given the industry's high turnover rates. But the Service Employees International Union, which represents more than 2 million workers in health care, janitorial and other industries, has been providing organizational and financial support to the push for higher pay over the past year.

In the meantime, Senate Majority Leader Harry Reid, D-Nev., has promised a vote on the wage increase by the end of the year. But the measure is not expected to gain traction in the House, where Republican leaders oppose it.