Doncaster MP Rosie Winterton joined other Labour MPs to vote against the controversial Bedroom Tax during a debate in parliament.
The tax, in which the government can limit housing benefit if you are deemed to have a spare room, has sparked protests nationwide.
The Liberal Democrats have now joined Labour in voting against their own policy in parliament.
The vote was won but it is unlikely to go any stage further. MPs voted as a way of putting the issue back in the public spotlight.
Doncaster Central MP Ms Winterton said: “Despite the clear evidence that the Bedroom Tax is causing misery, hardship and forcing thousands to rely on food banks, the Lib Dems and Tories have voted again and again in favour of it. If this government won’t ditch the Bedroom Tax, then the next Labour government will.”
The government said the policy is designed to bring social tenants into line with those living in privately rented properties on housing benefit.