The U.S. Department of Justice (DOJ) filed a lawsuit Thursday saying social media giant Facebook was discriminating against U.S. workers and hiring cheaper foreign workers instead.Many of the temporary workers the DOJ accused Facebook of giving hiring preferences to were foreign workers with H-1B visas.H1-B visas allow U.S. companies to hire foreign workers in “specialty occupations.” Critics say companies, particularly in technology, exploit the visa program to hire foreigners for less money.The DOJ further alleged that Facebook “refused” to consider qualified U.S. workers for over 2,600 open jobs paying an average annual salary of $156,000.The move came after a two-year investigation into Facebook’s hiring practices, The New York Times reported.“Our message to workers is clear: If companies deny employment opportunities by illegally preferring temporary visa holders, the Department of Justice will hold them accountable,” Eric S. Dreiband, assistant attorney general for the civil rights division, told the Times. “Our message to all employers — including those in the technology sector — is clear: You cannot illegally prefer to recruit, consider or hire temporary visa holders over U.S. workers.””Facebook has been cooperating with the DOJ in its review of this issue,” company spokesman Daniel Roberts told Reuters. “And while we dispute the allegations in the complaint, we cannot comment further on pending litigation.”Facebook CEO Mark Zuckerberg, with a personal wealth of about $100 billion, has long advocated for immigrants to work in the tech sector, the Times reported. In 2013, he created Fwd.us, a nonprofit advocating steps to make it easier to hire immigrants for technology jobs, according to the Times.The DOJ case against Facebook is another problem for Silicon Valley, which has come under fire in recent years for antitrust violations, anticompetitive practices, privacy concerns and content that some find offensive.