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Hundreds of protesters across the US marched Thursday to demand higher wages for fast-food workers, forcing the closure of one McDonald's in Detroit after its employees walked out.

The protests are underway in cities including New York, Boston and Chicago, and organizers are expecting the biggest national walkouts yet.

A McDonald's restaurant in Detroit closed Thursday morning as workers and protesters chanted "hey hey, ho ho, $7.40's got to go," outside, WJBK reports.

In New York, City Council Speaker Christine Quinn joined about 300 to 400 protesters in a march before flooding inside a McDonald's near the Empire State Building on Thursday morning. Shortly after the demonstration, however, the restaurant seemed to be operating normally and a few customers said they hadn't heard of the movement. The same was true at a McDonald's a few blocks away.

The lack of awareness among some illustrates the challenge workers face. Participating workers, who are asking for $15 an hour, still represent a tiny fraction of the industry. The federal minimum wage is $7.25 an hour, which works out to about $15,000 a year for full-time employees.

The movement comes amid calls from the White House, some members of Congress and economists to hike the federal minimum wage. But most proposals seek a far more modest increase than the one workers are asking for, with President Barack Obama wanting to boost it to $9 an hour.

In a wide-ranging interview with the Associate Press, Labor Secretary Thomas Perez said the strikes are another sign of the need to raise the minimum wage for all workers. He compared the protests to the demands of demonstrators in the 1963 March on Washington, who sought a national minimum wage to give workers better living standards.

"For all too many people working minimum wage jobs, the rungs on the ladder of opportunity are feeling further and further apart," said Perez, who's taking a lead role in Obama's push to boost the minimum wage.

The Service Employees International Union, which represents more than 2 million works in health care, janitorial and other industries, has been providing financial support and training for local organizers around the country.

Organizers say the strikes will hit more than 50 cities on Thursday, following a series of strikes that began last November in New York City. The biggest effort so far was over the summer when about 2,200 of the country's millions of fast-food workers staged a one-day strike in seven cities.

Ryan Carter, a 29-year-old who was walking out of the McDonald's where workers demonstrated on Thursday, said he "absolutely" supported workers demand for higher wages.

"They work harder than the billionaires in this city," he said. But Carter, who was holding a cup of the chain's coffee he bought for $1, said he didn't plan to stop his regular trips to McDonald's.

A few dozen people gathered along the street outside a McDonald's in Las Vegas, chanting and carrying signs that read "Strike for a living wage" and "Huelga por $15," Spanish for "Strike for $15." But an employee at the restaurants said it stayed open for business throughout the demonstration.

The latest protests follow a series of strikes that began last November in New York City. The biggest effort so far was over the summer when about 2,200 of the country's millions of fast-food workers staged a one-day strike in seven cities.

McDonald's Corp. and Burger King Worldwide Inc. say they don't make decisions about pay for the independent franchisees that operate the majority of their U.S. restaurants. At restaurants that McDonald's owns, the company said, any move to raise entry-level pay would raise overall costs and lead to higher menu prices.

"We respect our employees' rights to voice their opinions. Employees who participate in these activities and return to work are welcomed back and scheduled to work their regular shifts as usual," the company said.

It also noted that the protests didn't give an accurate picture of what it means to work at McDonald's. The company said it provides professional development for interested employees.

Wendy's said in statement that it was "proud to provide a place where thousands of people, who come to us asking for a job, can enter the workforce at a starting wage, gain skills and advance with us or move on to something else."

Starbucks spokesman Zack Huston said the strikes have not affected the company's stores. He noted that Starbucks employees earn "competitive wages" and affordable health care that other retailers do not provide for part-time workers.

Subway and Yum Brands Inc., which owns KFC, Taco Bell and Pizza Hut, did not respond to a request for comment.

Even though they're not part of unions, fast-food workers who take part in strikes are generally protected from being fired or having employers retaliate against them. Federal labor law gives all workers the right to engage in "protected concerted activities" to complain about wages, working conditions or other terms of employment.

"It's always been understood that people who fall under this concerted activity umbrella are protected as long as they are protesting not only on their own behalf but on behalf of others as well," said Robert Kaiser, a St. Louis labor law attorney.

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The Associated Press contributed to this report.