It claims that Facebook specifically did not advertise some roles on its careers website, which led to these specific roles having ~0 US applications. Whereas most other roles have hundreds of US applications.

What 'roles' were these? Is there some specific role they are not advertising?

Edit: The original complaint https://www.justice.gov/opa/press-release/file/1342786/downl... You are exactly right; there are no 'roles' and it stems from the completely different type of hiring exactly as you describe.

"Beginning no later than January 1, 2018, and continuing until at least September 18, 2019, Facebook’s standard operating procedure was to automatically initiate a PERM process when a temporary visa holder who was a Facebook employee in a “level 3” role1 or above asked Facebook for a permanent position, if the PERM process was needed to offer the PERM beneficiary such a position. 36. Facebook’s standard operating procedure was not to consider the temporary visa holder’s job performance or seniority or consult with the employee’s manager about the temporary visa holder’s job performance before initiating the PERM process on his or her behalf. 37. As noted above, to file a PERM application, Department of Labor rules first required Facebook to ensure that there were no minimally qualified and available U.S. workers for the position that Facebook wanted to offer to the PERM beneficiary. 38. From at least January 1, 2018 to at least September 18, 2019, when a Facebook employee who was a temporary visa holder expressed interest in receiving a permanent position through the PERM process, Facebook diverged from its normal recruiting protocols by not advertising the position on its external website, Facebook.com/careers, by not accepting online applications, and by requiring interested applicants to apply to the position by mail."

Essentially, it seems like when a temporary visa holder working at Facebook wanted to have a permanent position, Facebook would create a 'dummy' role for them, then advertise it where people would not apply, so that they could then hire the employee permanently. But I wouldn't call this discrimination at all; I would call this Facebook hiring as many talented people as they can, as fast as they can. The same 'role' is still available and on the careers website.