President Donald Trump vowed Thursday to investigate Twitter for their practice of “shadow banning” Republicans and conservatives.

“Not good. We will look into this discriminatory and illegal practice at once!” Trump wrote on Twitter. “Many complaints.”

Breitbart News has covered Twitter’s practice of hiding tweets and accounts of conservatives for over a year. On Monday, Breitbart’s Allum Bokhari reported on Twitter’s latest “shadow ban” attempt on his account and other Breitbart News reporters as well as prominent Republicans. Recently, left-leaning outlets have also reported on the issue.

A Twitter spokesman told VICE News Wednesday that their technology was based on “account *behavior* not the content of Tweets.”

VICE reported that Republican party chair Ronna McDaniel, Donald Trump Jr.’s spokesman Andy Surabian, and other conservative Republicans no longer appear in the auto-populated search box on Twitter.