By Tiffany Hsu, Los Angeles Times

Fast-food workers around the world rallied for a higher minimum wage Thursday in what organizers called the largest such protest of its kind.

The movement, which began as a single walkout in New York in 2012 before sprawling across the U.S. last year, will spark gatherings Thursday in 150 U.S. cities as well as 33 countries on six continents, according to planners.

Protesters are calling for a $15-an-hour minimum wage and the right to form unions without retaliation from bosses.

In the U.S., where union ranks are thinning, the fast-food strikes have been called an attempt by labor leaders to boost membership.

On Thursday, the libertarian Cato Institute said that paying fast-food workers $15 an hour could raise labor costs so much that companies will decide to slash headcount and boost menu prices. The right-leaning Employment Policies Institute said that nearly half a million workers nationwide could lose their jobs.

But protest participants say they want to emphasize that the demographic working the drive-throughs isn’t just teenagers looking for spending money. Instead, supporters say, employees are often heads of households, many of whom must resort to public assistance to supplement their salaries.

Some cities, counties and states are proposing or pushing through minimum-wage increases. In September, Gov. Jerry Brown signed a bill into law raising the minimum wage in California to $10 an hour by 2016. Earlier this month, Seattle Mayor Ed Murray unveiled his plan for a $15 minimum wage in the city.

On Thursday, social media filled with photos of crowds of protesters outside McDonald’s restaurants, Burger Kings and KFC outlets in New York, Ireland, India, Japan and elsewhere.

In Los Angeles, the Rev. Al Sharpton is expected to join demonstrators outside a Crenshaw Boulevard restaurant in the afternoon.

In a regulatory filing earlier this year, McDonald’s noted that “the impact of events such as boycotts or protests, labor strikes and supply chain interruptions” could “adversely affect” the company and its supply network.

In the same document, McDonald’s listed key factors that could affect its operations, plans and results.

On the list, the company placed “the impact on our margins of labor costs that we cannot offset through price increases, and the long-term trend toward higher wages and social expenses in both mature and developing markets, which may intensify with increasing public focus on matters of income inequality.”

In March, McDonald’s workers filed a spate of lawsuits against the company, accusing the burger giant of systematically stealing their wages and committing other labor violations.

steve rhodes via flickr