Passengers at stations including Edinburgh, London King's Cross, Peterborough, Newark, Doncaster, Durham, and Newcastle will be urged to support a campaign to keep the route under public control.
More than 60 MPs from the Labour, Liberal Democrat, Green and Scottish National (SNP) parties have signed an early-day motion calling on the Government to keep the line public.
The protest is timed to coincide with the start of the Liberal Democrat spring conference in York.
TUC general secretary Frances O'Grady said: "Privatising the East Coast defies all logic. Since it was re-nationalised the line has gone from strength to strength. This decision shows the government is clinging on to its outdated faith in privatisation at all costs and is determined to remain blind to the fact that public ownership has been a success for taxpayers and passengers alike.
"By taking the East Coast out of public ownership the Government will be passing the income the line raises into the pockets of corporate shareholders, when it should be using the cash to reduce rail fares and improve services for passengers."
Rail, Maritime and Transport union leader Bob Crow said: "The fact that the Lib Dems are lined up with their Conservative coalition bosses on the plans to take a wrecking ball to the highly successful, publicly-owned East Coast rail service helps explain their collapse in the opinion polls, as the British people see them as nothing but voting fodder for this rotten, right-wing government.
"This Conservative-led coalition will allow any nation state to run Britain's railways other than the British people themselves and the idea that East Coast, delivering the most successful and cost-effective rail services in the country, should be smashed apart in the interests of private greed will haunt this mob right up to polling day."
Mick Whelan, leader of the train drivers' union Aslef, said: "It's about time the Government, rather than rushing to privatise the East Coast Main Line before it is voted out of power next year, listened to the views of the travelling public and stakeholders in the industry, and left the East Coast in successful public ownership, returning money to the Treasury, rather than being siphoned off as private profit."
Transport Salaried Staffs Association general secretary Manuel Cortes said: "Nick Clegg should be ashamed of himself for supporting the Conservatives' crackpot idea for re-privatising the East Coast line on purely ideological grounds.
"As a publicly-run line, it has paid over £600 million to the Treasury and costs less to run than all the other private rail firms who rely on public subsidies to make profits."