With so many Labour rebels, the legislation will only pass with the support of the Conservatives without concessions.
Mrs Ellman said: “I agree that Royal Mail needs better management, but I am worried about it being privatised.
“I don’t think it is in the public’s interest, because there will be no guarantee the universal service will survive.
“I am also concerned about the future of Royal Mail’s facilities in Liverpool and I fear this proposal will make that situation worse.”
The other Merseyside MPs who are opposing the sell-off are: Joe Benton (Bootle), Frank Field (Birkenhead), Stephen Hesford (Wirral West), Peter Kilfoyle (Walton), Andrew Miller (Ellesmere Port and Neston), Eddie O'Hara (Knowsley South) and Bob Wareing (Liverpool West Derby).
Yesterday, 600 members of the Communication Workers Union (CWU) staged a protest rally in Westminster.
Ministers insist a private firm is needed to rescue Royal Mail after years of under-investment.
But there was anger when Lord Mandelson published a letter from the trustees of Royal Mail's pension scheme, warning its £5.9bn deficit would be unaffordable, should the sale be derailed.
It was seen as a non-too-subtle threat to slash pensions if the revolt continues.
