Sefton Central Labour MP Bill Esterson said the Lib Dem-led plan to sell off Royal Mail would lead to rocketing prices and scores of postal workers losing their jobs - including the potential closure of Maghull, Formby and Crosby sorting offices.
Lib Dem business secretary Vince Cable has drawn up the plans to sell Royal Mail to the highest bidder.
Bill Esterson warned that government's plans would damage the service.
Bill said: "Vince Cable is selling off a valuable asset which is owned by every single one of us, regardless of the views of the experts who say that costs will rocket, jobs will be lost and the service will suffer.
"The Lib Dems and the Tories have nationalised Royal Mail's liabilities in the form of the pension fund, but they are now pushing on with their ideological attack on all of our public services and privatising the profitable side of the service.
"Royal Mail’s overall operating profits more than doubled over the last year from £152m in 2011-12 to £403m in 2012-13. It is now that Vince Cable and the rest of his Lib Dem and Tory friends are ploughing ahead with their plans to sell it off.
"As with the East Coast Main Line, ideology has won out over common sense – it will be private investors who benefit from its commercial success not the taxpayer and most certainly not the customer."
Maghull Labour Councillor Patrick McKinley is a former Postal worker.
Cllr McKinley said: "Royal Mail is a fantastic public service which is owned by each and every one of us.
"The idea that the Lib Dems and Tories are working together to sell off something we all own is outrageous. It is a national asset and part of the fabric of British society.
"The latest G4S scandal shows the dangers of privatisation where profit is the main goal instead of public service.
"In the 1980s even Margaret Thatcher decided against privatisation of the Post Office which at that time was all part of the Royal Mail service. She said she wasn't prepared to sell off the Queen's head.
"Vince Cable is going further than Margaret Thatcher ever dared to."
Bill Esterson said he has spoken to a number of postal workers since the Lib Dem Business Secretary made his announcement on Tuesday.
Bill said: "I have been contacted by a number of concerned Royal Mail postal workers since Vince Cable made his announcement on Tuesday. Each and everyone of them have raised with me their concerns about these privatisation plans.
"They are offended by the offer of shares which they see as a bribe and they are worried about the future of the service that will affect every single one of us through rising prices and a poorer service.
"They predict an end to the universal service, which has seen a comprehensive six day delivery to anywhere in the UK for the same price, as a commercially run service will be run in the interest of profit at the expense of the customer.
"And they see this privatisation as a direct threat to their jobs.
"Royal Mail is a major employer in Sefton Central. It is the people whose jobs are on the line and the thousands of Royal Mail customers who rely on the service day in and day out that I represent.
"I strongly oppose these privatisation plans and I will be calling on Vince Cable and the rest of his Lib Dem and Tory colleagues in the Government to scrap the plans."
Bill and Cllr McKinley both said they would fight any plans to close the sorting offices in Maghull, Formby or Crosby.
Bill said: "One Royal Mail worker told us that Maghull sorting office would certainly face the threat of closure under these Lib Dem plans. First the police station, then the ambulance station, now it's our Royal Mail sorting office. All are being sacrificed at the altar of a dogmatic worship of the free market, where profits are made by a few wealthy individuals, while the many public sector workers face a fall in pay or loss of their jobs and the public see a massive cut in services."