Parliament's three post offices must not be exempt from the closure programme across the UK, an MP says.
Plans to close post offices have created an angry reaction
Tom Brake has put down a Commons motion saying London in particular will be "disadvantaged" by the government's programme to shut 2,500 branches.
It would not be fair if Parliament's post offices "all within 100 metres of one another" remained open, he added.
The Lib Dem MP's motion, also signed by Tory Bob Spink, came as No 10 repeated the need to "modernise" the network.
The Early Day Motion says cutting 170 branches in London means "hundreds of thousands of people will be affected by these closures because they may not be able to travel the extra distance to the next post office".
It adds that "whilst one fifth of London's post offices are being closed, the three Crown post offices in the House, all within 100 metres of one another, remain open".
The motion - of a type which allows MPs to express views rather than something which might become law - suggests that "Parliament should not be exempt from the disadvantage of post office closures".
Meanwhile, the Tories have accused several cabinet ministers of "rank hypocrisy" for campaigning to save post offices in their constituencies, despite the government's decision to back the closure policy last year.
Home Secretary Jacqui Smith and Justice Secretary Jack Straw are among those criticised.
Shadow post office minister Charles Hendry said the cabinet had "forced through a policy which is incredibly unpopular in communities up and down this country".
He added that Labour MPs were "queuing up to say that the access criteria are wrong; that individual post offices should close".
Jack Straw has defended his right to campaign on local issues
Mr Hendry also said: "Cabinet ministers above all have a responsibility to explain to their own constituency why those decisions were right, rather than just saying their constituencies should be exempted."
Post Offices Minister Pat McFadden told BBC Radio 4's Today programme that consultations about how post office closures would work locally were going on around the country.
He added: "I think it's right that MPs take part in consultations... that MPs of either party represent their constituents' views on this."
Mr Straw and Ms Smith were in the cabinet when the decision to go ahead with closures was taken in May last year.
Mr Straw met protesters last Friday in his Blackburn constituency.
His spokesman said: "It is perfectly legitimate for a Member of Parliament to make representations on behalf of his or her constituents.
"In talking to his constituents, Mr Straw made clear that the Post Office was facing considerable change and was under pressure from the internet and other changes.
"But he agreed to put the concerns of residents to Postwatch. As it happens in the case of Blackburn he thinks his constituents have a very strong case."
Ms Smith signed a petition against closures in her Redditch seat two years ago.
A spokeswoman said she fully accepted the need for post office rationalisation, but added that it proper for her to make representations on behalf of constituents.