© SpaceXA Falcon 9 rocket launches the Transporter-1 mission in January 2021.
The U.S. Department of Justice is investigating SpaceX over whether the company discriminates against non-U.S. citizens in its hiring practices and said Elon Musk's company is stonewalling a subpoena for information, court documents revealed Thursday.

The DOJ's Immigrant and Employee Rights Section received a complaint of employment discrimination from a non-U.S. citizen claiming that the company discriminated against him based on his citizenship status.

"The charge alleges that on or about March 10, 2020, during the Charging Party's interview for the position of Technology Strategy Associate, SpaceX made inquiries about his citizenship status and ultimately failed to hire him for the position because he is not a U.S. citizen or lawful permanent resident," DOJ attorney Lisa Sandoval wrote in a court document filed Thursday. The document was a request for a judge to order SpaceX to comply with an administrative subpoena for documents related to how the company hires.

SpaceX did not immediately respond to CNBC's request for comment. The Department of Justice declined to comment.

© AaronP/Bauer-Griffin | GC Images | Getty ImagesSpaceX headquarters in Los Angeles, California.
The Immigrant and Employee Rights Section, or IER, said it notified SpaceX via email on June 8 that it had opened an investigation, requesting SpaceX provide information and documents related to its hiring and employment eligibility verification processes.

The filing said SpaceX responded in August, sending the DOJ a Form I-9 spreadsheet of information about employees dating back to June 2019. But SpaceX refused the DOJ's request "to produce any Form I-9 supporting documentation, such as copies of employees' passports, driver's licenses, or Social Security cards," Sandoval wrote.

IER then obtained a subpoena on Oct. 7, but SpaceX refused to produce the subpoenaed documents, the filing said.

SpaceX filed a petition with a DOJ administrative tribunal to dismiss the subpoena on grounds that it exceeded the scope of IER's authority, but that petition was denied, and SpaceX was ordered to comply. IER said SpaceX on Dec. 11 acknowledged the order but told IER "that it 'does not intend to produce any additional information in response to the administrative subpoena.'"

The IER argued that the subpoenaed documents are relevant because they would show the extent to which SpaceX hires non-U.S. citizens, and that it's not a burdensome request, although SpaceX has told the IER that it would have to retrieve each document manually.

The Department of Justice is requesting an order from the court to require SpaceX to comply with the subpoena within two weeks.