Fast food workers were ratcheting up their call for higher wages Thursday with strikes planned in 100 US cities, labor advocates say. In the midst of the holiday shopping season, fast food workers are walking off their jobs and holding rallies across the country to draw attention to the wages, which start at the federal minimum wage of $7.25 per hour. Worker groups are calling for wages to more than double, seeking a minimum wage of $15 per hour. The New York Times reported Thursday that the average pay at a fast food outlet is $9 per hour, which would make $15 per hour a 67 percent raise. The worker advocacy organization Good Jobs Nation said the fast food industry employs, "an invisible army" of 2 million underpaid workers. "The effects of this invisible workforce are especially devastating for the local economy," the group said, calling for a rally at the Smithsonian's National Air and Space Museum McDonald's, where workers were expected to take part in the strike. The strikes began last year at a small number of restaurants and grew to 60 cities in a late-August strike. "I think there's growing recognition that a nerve has been touched. The industry had better start to take this seriously, because this isn't going to blow over.," said Mary Kay Henry, the president of the Service Employees International Union, a major sponsor of the fast food workers' movement. Restaurant owners have said the balancing point is jobs If wages soar, they would have to rely more on automation and less on paid workers, some have said. "When you start by insisting on $15 an hour, that's not conducive to substantive dialogue," said Scott DeFife, an executive vice president with the National Restaurant Association, the New York Times reported.