Martin Luther King Jr.'s "I Have a Dream" speech, given 50 summers ago, was his greatest address but far from his only one. We often overlook the fact that King talked about economic injustice as often as he spoke of social injustice. As we celebrate Labor Day, we should consider the message in another speech King gave that is not as well remembered but perhaps just as important.

In March 1968, King traveled to Memphis, Tenn., to support sanitation workers who had gone on strike for respect and the right to form a union. King congratulated the workers for taking a stand and asked, "What does it profit a man to be able to eat at an integrated lunch counter if he doesn't have enough money to buy a hamburger? What does it profit one to have access to the hotels of our cities, and the hotels of our highways, when we don't earn enough money to take our family on a vacation?"

Those questions still matter. And a new generation of workers is standing up to ask them. We've broken down many racial barriers, but too many working people of all races and ethnicities earn low wages and do not have financial resources they need to meet their basic needs.

That's why last week, thousands of fast-food and retail workers went on strike in stores across the country to call for a higher wage floor in their industries. They are not alone. This summer also saw historic actions by Walmart and warehouse workers.

Members of the Service Employees International Union are strongly supporting this movement. For far too many in this country, service work means poverty or near poverty. It is time to raise their pay.

It hurts all of us when companies hold down wages and take away benefits. Millions of solidly middle-class jobs were wiped out in the Great Recession. Now, even as corporate profits are surging back, good jobs are not returning. According to the National Employment Law Project, low-wage jobs made up 58 percent of positions added in the recovery. Five of the six fastest-growing jobs are in classifications that pay lower-than-average wages.

Fast-food jobs are no longer starter jobs for suburban teenagers. The average age of a fast-food worker may have been 22 a decade ago, but it is now 28. More than a quarter of fast-food workers are raising a child.

Jobs that pay low wages are a problem for all of us. As more families try to live off of jobs in fast food and retail, many of them cannot afford basics, like groceries, rent or transportation. They can't afford to spend and support small businesses and keep their local economies moving forward. Low wages choke off power to the engine of consumer spending that fuels our economy.

The model of paying CEOs tens of millions but average workers as little as possible costs us in other ways. Many Americans who work in service-sector jobs need assistance from public programs to keep food on the table for their families, get access to basic healthcare services, and keep a roof over their heads. All of us - taxpayers - are subsidizing corporate profits by paying for public services for employees who work hard but don't earn enough to afford their basic needs.

As we celebrate Labor Day and the recent 50th anniversary of the March on Washington for Jobs and Freedom, let us remember that the fight for racial, social and economic justice are inextricably linked. This is why labor leaders joined with civil rights leaders 50 years ago. We continue the struggle for social and economic justice for working men and women today. As King expressed so eloquently, what good is access to a lunch counter if you cannot afford to buy a sandwich? It's time for highly profitable companies to lift wages.

Mary Kay Henry is the president of the Service Employees International Union.

She wrote this for McClatchy-Tribune News Service.

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