Former Guardian editor Alan Rusbridger and other members of Facebook's oversight board are under growing pressure to speak out as the social network battles claims of hate speech.
The Supreme Court-style board-set up to rule on controversial ethical issues-has so far remained silent over a growing boycott by advertisers who are seeking tougher action on content which they believe promotes discrimination, hatred or violence.
Campaigners are now urging Mr Rusbridger and his colleagues to speak out.
Damian Collins, the former chairman of the Digital, Culture, Media and Sport Committee, said the silence of board members exposes its limitations.
He said: "It really demonstrates that no matter how many great and good people they recruit to join this oversight board, unless it has the power to initiate its own investigations and to make recommendations on changes of policy, then this will be a paper tiger."
The oversight board is due to begin operating later this year and will judge whether the social network's rules were applied correctly on its most controversial moderation decisions.
The board will be able to make policy suggestions, but Facebook retains a veto over any changes to the by-laws which govern how the body will function.
Decisions will also initially be limited to posts that have been taken down from Facebook rather than simply those that have been reported by users.
There are fears the group will be heavily influenced by Left-wing figures such as Mr Rusbridger, whose time in charge of the Guardian was characterised by its relentlessly anti-conservative views.
Concerns over hate speech on Facebook have led to a series of major advertisers pausing their ad spending on Facebook for July. Companies including Microsoft, Ford and Adidas have joined the boycott. Two leading UK firms-insurer Aviva and Intercontinental Hotels-have also recently joined it.
Facebook had attempted to head off the crisis by announcing new curbs on hate speech in political adverts, but activists and some companies dismissed them as insufficient.
Accountable Tech, an American non-profit organisation, announced on Tuesday that it had begun a new campaign urging members of the oversight board to either speak up and request expanded power over Facebook, or step down from the board.
The group will spend $25,000 (£20,000) on online adverts urging members of the board to speak up about the issue.
Nicole Gill, the group's executive director, said: "It's unacceptable for the board to be sidelined and escape scrutiny."
Ms Gill said she hopes the group's campaign "will make some of these members reconsider whether they want to be used for cover as Facebook maintains their broken status quo - we really do hope they'll either demand real authority to tackle the urgent issues at hand, or walk away".
Dex Hunter-Torricke, the head of communications at Oversight Board Administration, said: "Hate speech is one of the issues that the oversight board will be considering when we go operational later this year, and we won't shy away from the tough cases and holding Facebook accountable.
"For a board focused on deeply challenging content questions impacting a global community, we believe it's important to build this institution with care while moving as quickly as possible."