A poster mocking the apparent ages of child refugees entering the UK was pinned up in Parliament.
The image, which shows an elderly man with the text "Just £3 from you could clothe and feed this 12yr old Syrian child for a week", was placed above a sink in a communal kitchen.
Chi Onwurah, the Labour MP for Newcastle upon Tyne Central, tweeted a picture of the poster and branded it "xenophobic".
Ms Onwurah, the shadow minister for industrial strategy, said: "I think it demonises and dehumanises Syrian migrants - I think that is xenophobic.
"To demonise and reduce people fleeing Syria, when we've seen what they are going through, to a meme basically saying they are liars and dishonest - I think it is offensive.
"I want to make sure it doesn't happen again and I want to make it clear that it isn't acceptable."
The poster was found this morning by her researcher Sarah Pine, who said the communal kitchen serves 17 MPs from Labour, the SNP and the Conservative party, as well as their staff.
Its discovery comes as the clearance of the Jungle camp in Calais began and a row continued over the apparent ages of child refugees.
Tory MP David Davies questioned the ages of refugees entering the UK as under 18s and said dental checks should be carried out to determine how old they are.
Critics, including the former footballer and Match Of The Day presenter Gary Lineker, hit out at the treatment of child refugees.
Mr Lineker faced calls to be sacked for calling some critics "hideously racist" to which he responded by tweeting: "Getting a bit of a spanking today, but things could be worse - imagine, just for a second, being a refugee having to flee from your home."