FILE - Union members picket  outside the Trump Taj Mahal caino in Atlantic City, N.J.
FILE - Union members picket outside the Trump Taj Mahal caino in Atlantic City, N.J.

"When workers raise their voices for a fair wage and dignity in the workplace, they sustain the story of America," U.S. President Barack Obama wrote Monday in an open letter to workers across the country as the U.S. celebrates Labor Day.

Labor Day became an official American holiday in 1894. It is observed on the first Monday in September.

"At the beginning of the last century, American workers came together to fight for dignity and justice in the workplace," Obama said.  "They stood up, marched and raised their voices for a 40-hour workweek, overtime pay, a minimum wage, and the right to organize for better pay and benefits . . .  These hard-fought victories became the cornerstones of the greatest middle class the world has ever known."

The president said if he were looking for a job today that would allow him to "build some security for my family, I'd join a union."

"History shows that working families can get a fair shot in this country - but only if we are willing to organize and fight for it... That's why I started my career as an organizer all those years ago," Obama said.

WATCH: Obama's message to American workers on Labor Day



While the membership rosters of labor unions have been falling steadily for the past 30 years, workers' benefits the unions fought for decades ago are now customary in most U.S. workplaces, including five-day work weeks, healthcare insurance and vacations paid for by employers.

Many union members now work for local, state and federal governments in white-collar jobs, not in the gritty factories where the labor movement began.