The House of Commons must "stop funding hate" by immediately pulling its advertising on right-wing news websites such as Breitbart, says a Yorkshire MP.
Mary Creagh MP, a one-time Labour leadership candidate, said adverts promoting free tours of the Houses of Parliament should be "removed immediately" from Breitbart, a controversial online news syndicate that is popular in the US and has a UK presence.
An image from breitbart.com shared by Wakefield MP Ms Creagh shows an advert that reads: "Snap up your FREE visit to UK Parliament".
Parliament has already confirmed its advertising policy is being reviewed following the discovery of its marketing appearing on the website.
Breitbart News was once described by Bloomberg as "a haven for people who think Fox News is too polite and restrained" and Ms Creagh called it an "extreme, far-right, white supremacist fake news website".
Steve Bannon, formerly US President Donald Trump's chief strategist, was previously Breitbart's executive chairman and positioned it as a platform for the alt-right.
The chairman of the environment audit committee has written to Jacob Rees-Mogg, the Leader of the Commons, calling on him to personally intervene to stop Parliament's advertising appearing on "such websites in the future".
"I am writing to you about the appearance of House of Commons adverts on Breitbart, to ask that they are removed immediately, and for you to ensure that the House's ads do not appear on such websites in the future," said Ms Creagh.
"The Stop Funding Fake News Campaign have spotted that adverts for tours of Parliament have been hosted on Breitbart, the extremist, far-right, white supremacist fake news website set up by Steve Bannon.
"A quick tour of the site reveals it is a home to misogyny, homophobia, anti-Semitism, Islamophobia, racism and wild conspiracy theories.
"Macmillan Cancer Support, the WWF and eBay are some of the organisations which have already blacklisted fake news sites like Breitbart, Evolve Politics, Rebel Media, The Canary, Politicalite, Dorset Eye, and Westmonster."
The Wakefield MP asked Mr Rees-Mogg: "Will you ensure that Parliament stops funding hate by ensuring the House removes its ads, and holds a review into how this regrettable incident occurred?"
Copies of the correspondence have been sent to Speaker John Bercow, shadow Commons leader Valerie Vaz and Sir Paul Beresford MP, chairman of the administration committee.
A UK Parliament spokesman said: "As part of our democratic engagement strategy to widen access to Parliament, we often use online advertising to promote visits and tours.
"Our digital marketing agency, as is standard practice, uses an entirely automated system which uses an algorithm to match adverts with likely interested audiences, in this case those with an interest in politics.
"However we have now paused these adverts and are reviewing our digital advertising policy".