Bob Crow, the general secretary of the Rail, Maritime and Transport union, is to call today's rally in London "a building block towards the objective of co-ordinated action and a general strike".
Public and Commercial Services union leader Mark Serwotka will also call for co-ordinated strikes to be held as soon as possible after today's protest.
The TUC general secretary Brendan Barber is to accuse the Government of "broken promises" when he addresses a major rally in London later today.
He will say: "Ministers told us that if we only accept the pain, recovery would come. Instead we have been mired in a double dip recession.
"They told us if we only accepted the cuts, our deficit would come down. Instead our borrowing is going through the roof.
"The biggest lie of them all was the cynical double talk that we are all in this together. The grim reality has been tax cuts for the richest with wage and benefit cuts for the poorest."
Tens of thousands of workers, anti-war campaigners, politicians, community groups and other activists are expected to join a huge rally to protest against Government spending cuts in London today.
More than 250 coaches have been booked to bring people to London, while similar protests will also be held in Belfast and Glasgow.
The Labour leader Ed Miliband will be among dozens of speakers at a rally in Hyde Park, joining union officials who will spell out the impact of spending cuts on public services.