Where two companies appear to have virtually identical shares in their relevant markets, it is an abuse of discretion for an agency to allow only one of the two to charge market rates without stating a reasonable justification for the distinction.
https://www.cadc.uscourts.gov/internet/opinions.nsf/9E0C54378AB5C5A18525830F004E9C61/$file/16-1285-1751902.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.