Respect wants an end to public service cuts (PIC: Richard Searle)
Respect have set out their conditions for supporting a Labour government in a hung Parliament.
As they launched their manifesto the party said they would not back a Tory government "under any circumstances".
But they would support Labour if troops were withdrawn from Afghanistan, more council houses were built, there was electoral reform and an end to cuts.
The anti-war party is hoping to gain up to three MPs on 6 May, which could leave it holding the balance of power.
Launching its manifesto at the Friends Meeting House in Manchester, national chair, Dr Kay Phillips, said Respect shared many policies with the Green Party and would work with them in the Commons if leader Caroline Lucas succeeded in her aim of becoming the first Green MP.
"There could be a grouping of about five left-of-Labour MPs within Parliament if there was a hung Parliament," she said at the party's manifesto launch.
"There are certain things we would be looking towards, such as bringing the troops home from Afghanistan and stopping cuts in public spending, building more council homes and green jobs."
Respect, which was formed in 2004 out of the anti-Iraq war movement, believes three of its candidates - George Galloway in Poplar and Limehouse, Abjol Miah in Bethnal Green and Bow, and party leader Salma Yaqoob in Birmingham Hall Green - have a good chance of being elected on 6 May.
Dr Phillips, a GP in North Manchester, who is standing in the new constituency of Blackley and Broughton, urged anti-war voters not to back the Lib Dems, who also opposed 2003's invasion of Iraq.
"I don't trust the Lib Dems because they were against the Iraq war, but the minute it started they were in favour of it. We were still against the war."
She said the party was also dedicated to fighting racism and was standing candidates across the North-West.
The party's manifesto vows to break what it calls the "cuts consensus" of the the three main parties.
Protect services from cuts
Celebrate multi-cultural Britain
Troops home from Afghanistan
It claims the country is not as broke as Labour, the Conservatives and the Lib Dems claim, with George Galloway - elected as a Respect MP in 2005 - saying in the manifesto the deficit was higher in 1945 and "in every year through to the 1960s".
Mr Galloway says the party would demand an "early date for withdrawing British troops from the bloody and pointless wars in Iraq and Afghanistan", scrap Britain's nuclear weapons and invest the money saved in protecting hospitals, schools and other public services from cuts.
Respect's leader Salma Yaqoob, who was not at the launch, said: "Respect stands for a positive, progressive way forward in British politics.
"Whilst the mainstream parties fight over who would implement the most cuts to the vital public services on which we all rely, Respect would invest and defend those services.
"Our policies aim to build a future of peace, justice and equality."