Sen. Ted Cruz (R-Texas) sent a letter to the nonprofit operator of Wikipedia alleging a pattern of liberal bias in articles on the collaborative encyclopedia.

“I write to request information about ideological bias on the Wikipedia platform and at the Wikimedia Foundation,” Cruz wrote to Wikimedia Foundation CEO Maryana Iskander in a letter dated October 3. “Wikipedia began with a noble concept: crowdsource human knowledge using verifiable sources and make it free to the public. That’s what makes reports of Wikipedia’s systemic bias especially troubling.”

Citing research from the conservative Manhattan Institute, Cruz wrote that “researchers have found that articles on the site often reflect a left-wing bias.” Cruz alleged that “bias is particularly evident in Wikipedia’s reliable sources/perennial sources list” because it describes “MSNBC and CNN as ‘generally reliable’ sources, while listing Fox News as a ‘generally unreliable’ source for politics and science. The left-wing Southern Poverty Law Center gets a top rating, but the Heritage Foundation, a prominent conservative think tank, is a ‘blacklisted’ and ‘deprecated’ source that Wikipedia’s editors have determined ‘promotes disinformation.’”