FOR the past two years, Sean Caldwell, of Mount Airy, has been struggling to support himself and raise his children on his $8-an-hour part-time salary on the maintenance crew at McDonald's at Broad and Allegheny, in North Philly.

It just hasn't been nearly enough - so he scrounges for whatever else he can.

Caldwell, 35, started a neighborhood lawn-mowing business and takes other odd jobs, such as cleaning out garages, but when he did his 2013 taxes he still saw that he'd made only $9,000. To bridge the gap, Caldwell, like many workers in the fast-food industry, received food stamps and other taxpayer-funded benefits, such as Medicaid.

This December, Caldwell saw a cable-TV news report about workers from McDonald's and other fast-food restaurants in New York City staging a one-day strike. "I was excited - I wanted to see where this thing could go, if it could gain traction," he said. "I said, 'I sure hope it comes to my city!' "

This week, Caldwell gets his wish. For the past month, scores of fast-food workers and labor organizers have been working behind the scenes to finally bring the national fast-food-workers movement - which seeks a raise to $15 an hour and the right to unionize - to Philadelphia. It's tentatively scheduled to kick off tomorrow with a job action outside McDonald's on Broad Street near Girard Avenue.

Leaders of the Fast Food Forward movement - part of a broad coalition of labor and community groups that has staged one-day strikes and pickets in about 200 cities - now hope to place Philadelphia at the vanguard of a push to raise the minimum wage and address America's growing income gap.

'One shot in history'

"This is their one shot in history to ultimately change the conditions they live and work in," said Kendall Fells, the national organizing director for Fast Food Forward. The group recently brought to Philly some fast-food workers who'd staged job actions in Pittsburgh, to motivate local would-be activists like Caldwell.

The launch of a fast-food-workers movement in Philadelphia comes as the less-than-2-year-old effort has moved onto the front burner of American politics, claiming a few small victories.

Earlier this year, President Obama made a call for a $10.10 minimum wage the centerpiece of his State of the Union address, stating that "too many Americans are working more than ever just to get by, let alone to get ahead." The president also mandated a $10.10 pay floor on some federal contracts - a move that's been echoed by a handful of private employers, including retail giant Gap, which recently announced a starting salary of $10 an hour.

The push comes amid growing evidence that fast-food jobs - once meant to be a stepping-stone for teens and others entering the labor market - have become the primary source of income for a growing number of adults, many of them raising a family. What's more, researchers say that U.S. taxpayers are footing the bill for food stamps, Medicaid and other forms of welfare to fill the gap between what these workers earn and what it costs to survive.

A study last year by researchers at the University of California, Berkeley, and the University of Illinois found that 52 percent of fast-food workers receive some form of government assistance and that the annual cost to taxpayers is nearly $7 billion. The report was subsidized by Fast Food Forward, but other studies have found similar numbers.

Ken Jacobs, chairman of the UC Berkeley Labor Center who worked on the study, said that the team found more fast-food jobs going to adults with children than to teens living at home because of vanishing middle-income openings. "Coming out of the recession, we've seen more opportunities for low-wage service workers and for high-income professionals - with the middle-income jobs disappearing," he said.

'Not counting $100 bills'

But a lobbyist for the restaurant industry in Pennsylvania said that the demand for a $15 wage just doesn't jibe with the profit realities of the fast-food business here - that many franchisees might have just one or two franchises, clearing perhaps $50,000 apiece.

"They're not counting hundred-dollar bills in some back room," said Melissa Bova, public-affairs representative for the Pennsylvania Restaurant & Lodging Association.

Bova also said that Fast Food Forward and allied groups were gaming the country's labor rules by essentially organizing workers but not in the guise of a union, which would trigger certain labor-law restrictions.

"Businesses are playing by the rules, and these organizations aren't," she said. In Philadelphia, Fast Food Forward is working closely with organizers at the 120,000-member Local 32BJ of the Service Employees International Union, or SEIU, as well as such community groups as Youth United for Change.

CEO's salary tripled

Advocates for the fast-food workers say that multiple studies have shown that a higher minimum wage - compared with a neighboring jurisdiction - does not lead to job losses, that the impact on the price of menu staples like a hamburger would be negligible and that workers deserve a break today, just like new McDonald's CEO Don Thompson, whose salary tripled when he took the job in 2013 to $13.8 million a year.

"With $15 and a union I could take care of myself and be able to live and able to save money," said Robyn Richardson, a sandwich-maker at Jimmy John's, in Center City, who joined the Philadelphia fast-food movement after learning about it through a YouTube video that a friend sent to her. "I don't know what savings are, because I live paycheck to paycheck."

Richardson, 22, a graduate of Pottstown High School, said that she and her 11-month-old son - who squirmed in his pajama bottoms and a gray coat while his mom was interviewed at a Logan restaurant - will lose their health insurance when he turns 1 in a few weeks.

Living with a sister nearby and eager to begin classes this fall at the Art Institute of Philadelphia, Richardson also receives food stamps and says that it's a struggle - especially when the nearest grocery store selling cheaper baby formula is not close by. With a raise, she said, "I wouldn't have to struggle to buy diapers."

Both she and Caldwell agree that working in a fast-food restaurant is fast-paced, hectic, on-your-feet labor, but their main complaint - in addition to low wages - is the unpredictability of their work schedules. They frequently get scheduled for 30 hours a week or less, or lose hours by being sent home early on slow days - and they worry that if they call out sick their hours might get reduced.

Not surprisingly, there are complicating factors. Caldwell, a graduate of Bishop McDevitt High School, in Montgomery County, who's worked a variety of jobs while seeking a Harcum College associate degree, has fathered eight children, two of whom live with him. He concedes to some "immature decisions, but I don't regret any of my children." He said he sees all of them every week, while he decides whether to pay for a son's football trip or instead for bunk beds for three girls who now must sleep together.

"I'm always robbing Peter to pay Paul," said Caldwell - but he, Richardson and other advocates for fast-food workers say that a higher living wage and a union would mean better worker morale, which would translate into better customer service and more sales.

They worry about risks of a one-day strike, but insist that it's a battle worth waging.

"If you don't fight for it," said Caldwell, "you're not going to get it - not in this capitalistic system."

On Twitter: @Will_Bunch