On Thursday, fast-food workers in more than 30 countries across six continents will take coordinated action on an unprecedented scale. In the United States, they will walk off their jobs in 150 cities — the largest strike ever. Workers around the world will join these protests in 80 cities.

The protestors are set to take over a McDonald’s during lunchtime rush hour in Belgium; hold flash-mobs at McDonald’s restaurants across the Philippines, and conduct a teach-in at McDonald’s headquarters in New Zealand.

The spread of the fast-food movement to the global stage is notable for the speed at which it has happened. What began as a single strike in New York City in November 2012, with roughly 200 workers participating, has in 18 months spread across the country and now across national borders. The efforts of fast-food workers have captured the nation’s attention, been featured in President Barack Obama’s speeches on inequality and inspired local elected officials to raise minimum wages.

The worldwide reach of the movement spells trouble for fast-food corporations. The sight of Japanese and Indian workers joining their counterparts in the U.S. protest should leave these corporations shuddering.

While U.S. fast-food sales are stagnant or declining, revenues overseas are surging. The industry’s international footprint has increased dramatically in recent decades into a global profusion of U.S. fast-food restaurants.

More than half of Subway’s new stores in 2013, for example, were opened outside the United States. McDonald’s overseas sales have outpaced domestic results for some time, with the majority of the company’s revenue coming from Europe and Asia.

Fast food’s future is clearly global. Hamburgers and milkshakes are increasingly common in cities from Buenos Aires to Beijing, and their growth shows no signs of slowing. International fast-food restaurants are expected to expand at four times the rate of U.S. businesses, according to a recent Merrill Lynch report.

That’s why it was so significant last week when workers from Argentina, New Zealand, Denmark and dozens of other countries joined for the first time to plot a global fast-food organizing strategy. Ron Oswald, president of the International Union Federation that orchestrated the meeting, said it was only the beginning of an international fast-food worker movement.

In the United States, McDonald’s has expressed concern about the protests, warning investors it might have to raise wages this year because of them. Company executives responded to class-action suits alleging widespread wage theft by launching a comprehensive internal investigation. They have also been monitoring the websites of the protest movement, according to internal emails reviewed by the Wall Street Journal.

If the worker movement prompts this much concern in a country where sales are slumping, imagine the level of alert once it reaches countries that are key drivers of fast-food corporations’ growth.

That is where the focus is — in Japan, where workers will protest at 30 different McDonald’s in 30 different prefectures; Brazil, where employees will rally at restaurants in five different states; and in Britain, where a 20-city protest will launch that nation’s Fast Food Rights campaign.

Thursday’s strikes and protests mark more than international solidarity among fast-food workers. They are borne of the same set of circumstances — low pay, erratic scheduling, few benefits and persistent violations of rights. Though the workers may speak different languages, their struggles of raising a family on poverty pay are often universal.

As we’ve seen in the United States, until fast-food corporations recognize this reality and raise wages, they’ll continue to face growing worker unrest – and threats to their bottom line.

PHOTO (TOP): Demonstrators gather during a nationwide strike and protest at fast food restaurants to raise the minimum hourly wage to $15 in New York, December 5, 2013. REUTERS/Shannon Stapleton

PHOTO (INSERT 3): Chinese queue outside the new Mcdonald’s restaurant in Xian, Shaanxi province, August 31, 2001. REUTERS/Files