America's 22,790 air-traffic controllers have gone unpaid since the government shutdown began on December 22.The National Air Traffic Controllers Association sued the federal government on January 11 for "unlawfully depriv(ing)" its union members of wages.One air traffic controller said she was unable to attend her grandmother's funeral during the shutdown as she hasn't been paid for weeks.Two other federal employee unions have sued the government since the shutdown commenced.The union that represents America's 22,790 air-traffic controllersis suing the federal government.The National Air Traffic Controllers Association (NATCA) is alleging that "the government unlawfully deprived NATCA members of their earned wages without due process," and thus violated the Fifth Amendment.On January 11, according to the NATCA's motion, air-traffic controllers and other NATCA members should have been compensated for the first pay period of 2019. But, as some air-traffic controllers posted on Twitter this week, their pay stubs reflected a take-home pay of no more than $0.Read more: Air-traffic controllers working unpaid during the government shutdown are posting their $0 pay stubs on TwitterNeither NATCA nor its legal counselMolly Elkin, partner at Woodley & McGillivary LLP, immediately returned Business Insider's request for a comment. The White House also did not respond.The suit also argues that the federal government violated theFair Labor Standards Act for not paying air-traffic controllers and other NATCA members at least minimum wage or overtime pay.As Business Insider's Benjamin Zhang reported yesterday, air-traffic controllers who are working unpaid are due to receive back pay once the shutdown ends. Furloughed workers might not receive any pay.The shutdown has hurt air-traffic controllers in ways that won't be addressable through back pay, the suit alleges. One NATCA member said she couldn't afford travel to her grandmother's funeral on January 8, and others could not afford urgent medical care for their family members."Measuring the weight of these individual losses as they are multiplied across the thousands of Air Traffic Controllers represented by the NATCA becomes unbearable; a continued deprivation of rights is not sustainable for NATCA's members, who already serve the nation in one of the most stressful jobs in the country," the case describes. "These are losses for which future monetary compensation is insufficient."Air-traffic controllers earn a median of $124,540 per year. There's already a shortage of controllers, and the job requires four years of training.Since the shutdown began on December 22, some 420,000 federal employees are working without pay. Transportation Security Administration (TSA) workers are experiencing "extreme financial hardships" as they're working without pay, and some have quit. Many TSA employees are calling in sick as they lack the funds to get to work.Read more: Delta, United, and JetBlue pilots are warning that flying will become more dangerous as the government shutdown continuesTwo other government worker unions have sued the federal government since the shutdown began.National Treasury Employees Union sued the federal government on January 9 as workers represented in their union also went unpaid. The NTEU represents 150,000 employees across 33 government agencies and departments,tens of thousands of which have worked unpaid during the shutdown.TheAmerican Federation of Government Employees, a union that includes correctional officers, Border Patrol and ICE agents, sued the US government on December 31for requiring employees to labor without pay.SEE ALSO:As TSA agents go unpaid, Travis Scott and Kanye West songs are blasting through JFK's loud speakersJoin the conversation about this storyNOW WATCH: Here's what it's like to drive trains on London's Tube ' one of the most complicated subway systems in the world Click here to read full news..