The US government has filed a lawsuit against Facebook, accusing the social media giant of "intentional and widespread" violations of the laws to discriminate against American workers and favour H-1B visa holders.

H-1B is a non-immigrant visa that allows US companies to employ foreign workers in speciality occupations that require theoretical or technical expertise. Most of the nearly 600,000 H-1B visa holders are from India and China.

The lawsuit, filed on Thursday by the Justice Department, alleges that Facebook refused to recruit, consider or hire qualified and available US workers for over 2,600 positions and instead, reserved for temporary visa holders it sponsored for permanent work authorisation (or "green cards") in connection with the permanent labour certification process (PERM).

The PERM process requires an employer to first demonstrate that there are no qualified and available US workers for the position that the employer plans to offer to the temporary visa holder.

The positions that were the subject of Facebook's alleged discrimination against US workers offered an average salary of approximately USD 156,000.

According to the lawsuit, which followed a nearly two-year investigation by the Justice Department, Facebook intentionally created a hiring system in which it denied qualified US workers a fair opportunity to learn about and apply for jobs that the company instead sought to channel to temporary visa holders.

"The Department of Justice's lawsuit alleges that Facebook engaged in intentional and widespread violations of the law, by setting aside positions for temporary visa holders instead of considering interested and qualified US workers, said Assistant Attorney General Eric S Dreiband of the Civil Rights Division.

"This lawsuit follows a nearly two-year investigation into Facebook's practices and a reasonable cause' determination by the Justice Department's Civil Rights Division. 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, he said.

According to the complaint, between January 1, 2018, and September 18, 2019, Facebook employed tactics that discriminated against US workers and routinely preferred temporary visa holders, including H-1B visa holders, for jobs in connection with the PERM process.

Rather than conducting a genuine search for qualified and available US workers for permanent positions sought by these temporary visa holders, Facebook reserved the positions for temporary visa holders because of their immigration status, it said.

The complaint also alleges that Facebook sought to channel jobs to temporary visa holders at the expense of US workers by failing to advertise those vacancies on its careers website, requiring applicants to apply by physical mail only, and refusing to consider any US workers who applied for those positions.

In contrast, Facebook's usual hiring process relies on recruitment methods designed to encourage applications by advertising positions on its careers website, accepting electronic applications, and not pre-selecting candidates to be hired based on a candidate's immigration status, according to the lawsuit.

The complaint seeks civil penalties, back pay on behalf of US workers denied employment at Facebook due to the alleged discrimination in favour of temporary visa holders, and other relief to ensure the company stops the alleged violations in the future.

Meanwhile, Facebook in a statement said it "has been cooperating with the DOJ in its review of this issue and while we dispute the allegations in the complaint, we cannot comment further on pending litigation".

President Donald Trump has been raising concern for years about foreigners competing with American citizens for jobs. In June, the Trump administration extended a ban on green cards issued outside the US until the end of the year and added many temporary work visas to the freeze.

On Tuesday, a US court blocked two H-1B regulations proposed by the Trump administration to restrict the ability of American companies to hire foreign employees.

In his 23-page order, US District Judge Jeffrey White of Northern District of California blocked the Trump administration's recent policy that required employers to pay foreign workers on H-1B visas significantly higher wages. He also set aside another policy that narrowed the eligibility of H-1B valued by US tech firms and other employers.