Left-wing advocacy group Media Matters for America has been quietly working with social media giant Facebook to combat what the group describes as "propaganda" and "fake news," internal documents reveal.

Media Matters told current and prospective donors at a retreat in Florida over the weekend that it has been in discussions with Facebook leadership about their policies on inaccurate and partisan news stories on the website that many liberals blame for political losses last year.

"We've been engaging with Facebook leadership behind the scenes to share our expertise and offer input on developing meaningful solutions," the group said in a briefing book obtained by the Washington Free Beacon at the conference.

"Media Matters will serve as their partner," the group said of its work with Facebook and other social media companies.

Conservatives have argued in the past that Facebook intentionally marginalizes right-leaning voices, a theory that could be fueled by the social media network's ties to Media Matters, among the harshest critics of conservative figures and ideas.