On Monday morning the business secretary told BBC Radio 4's Today programme that he could "certainly welcome" Ed Miliband and Ed Balls' call for a new levy on houses worth £2m, a long-held Lib Dem policy, if it was "real".
Labour published the text of its motion on Friday, however Cable told the BBC he had yet to take a look at it.
Cable said: "Well I haven’t seen the motion that they’ve put forward and I think we’ve always said that it depends how they phrase this and we’ll certainly have a look at it."
He added: "If it is a real commitment I would certainly welcome that."
"Nick Clegg and I are very strong supporters of the mansion tax and indeed it was a prominent feature of the Eastleigh by-election, but these Opposition days in parliament, they’re about positioning rather than policy making," he said. "We’ll have a look what the Labour motion actually says."
Asked whether the coalition would present a united front during the Commons debate, David Cameron's official spokesperson said: "The prime minister expects government ministers to support the government in tomorrow's vote."
Ahead of tomorrow's vote the Tories and Lib Dems are said to be working on a amendment to the Labour motion that both Conservative and Lib Dem MPs can support.
Lib Dem MP Julian Huppert, who also said he had yet to see Labour's motion, said he had not yet decided which way to vote but expected Labour was simply causing mischief. He told HuffPost UK: "I haven't seen the motion, I fear they are playing parliamentary silly buggers."
The vote is win-win for Labour. Should the Lib Dems decide to make a stand and support the motion, which after all was their policy in the first place, Miliband can claim to have split the coalition on a hugely symbolic issue.
But if the junior coalition partner decides to stick with the Tories and vote down the motion, it allows Labour to attack them for abandoning their principles.
On Sunday Lib Dem education minister David Laws, a close ally of Nick Clegg, indicated the party leadership would ask its MPs to vote against Labour.
"If we flounced off every time an opposition party, often for opportunistic reasons, put down motions in the House of Commons that either backed the Tory position or the Lib Dem position we would end up in a complete shambles," he said.
"So, we have to agree policy for each Budget with our coalition partners. Sometimes we get the things we want, sometimes we don't, but that is the right way to make policy in a coalition government."
The Labour motion to be debated on Tuesday reads:
"That this House believes that a mansion tax on properties worth over £2million, to fund a tax cut for millions of people on middle and low incomes, should be part of a fair tax system and calls on the Government to bring forward proposals at the earliest opportunity."Suggest a correction