Demonstrators march during a protest against police violence towards minorities in Downtown Manhattan, New York January 15, 2015. [Photo/Agencies]

At Philadelphia International Airport, about 100 non-unionized airport workers marched silently through four terminals to a designated "free speech zone" where they held a rally accusing contractors of ignoring minimum wage rules.

Similar protests were planned at airports in Boston and Fort Lauderdale in Florida, organizers said.

All told, some 12,000 people work for cleaning, baggage handling, security and other service contractors at the three major airports serving New York City, according to the Local 32BJ of the Service Employees International Union, most of them earning $9 per hour.

New York's minimum wage is $8.75 an hour for most jobs. The Port Authority of New York & New Jersey, which runs the airports, ruled last year that its contractors must pay at least $10.10 an hour to most airport workers starting in February, a Port Authority spokeswoman said.

Speaking to marchers before they set off, US Representative Charles Rangel, a New York Democrat, described economic disparities in the United States as "a disease."

"It's morally wrong to leave those behind that are making America economically strong," he told the crowd.