The motion, which was opposed by the union's leadership, was backed by 478,888 votes to 386,226 - a majority of more than 90,000.
The vote reflects concern among Unison members about the Labour government's plans to increase the involvement of the private sector in public services.
Unison general secretary Dave Prentis said: "This motion calls for a review of both our affiliated political fund and our general political fund.
"We are happy to carry out that review.
No change
"The vote does not change in any way whatsoever our arrangements with either the Labour Party or our general political campaigning work."
Mr Prentis pointed out that the conference had earlier "roundly defeated" a proposal to withhold cash from Labour if the government failed to halt the use of the private finance initiative.
On Tuesday, Stephen Byers was heckled while making a speech at the union's conference
The new secretary of state for transport, local government and the regions came under fire over government plans to allow greater use of private finance in the public sector.
Difficulties
After the cash vote a union spokesman said that the result reflected difficulties members have with that issue.
The motion, which was titled "The Labour government - what do we get for our money", said that despite four years of a Labour government, Unison members continued to face cuts in jobs and conditions.
Privatisation of public services had continued apace under Labour and hundreds of thousands of people earned less than £5 an hour.
"Conference notes that, increasingly Unison members are asking why we hand over millions of pounds of members money to fund a party who is attacking our jobs, wages and conditions," said the motion.