Just days before a Senate vote, the government is battling on two fronts with a Liberal senator threatening to cross the floor and the Greens unable to commit to a deal because of internal division.

Despite Greens leader Richard Di Natale and education spokeswoman Sarah Hanson-Young's work to secure major concessions from the government, there remains strong resistance from Greens MPs to any deal that would anger public sector teacher unions.

The government had been growing increasingly confident it could pass its changes without the Greens by securing the votes of the One Nation senators, Nick Xenophon Team and three other crossbenchers.

But that was thrown into doubt on Monday by a declaration from WA Liberal Senator Chris Back, a passionate supporter of Catholic education, that he had not been convinced to vote for the bill.

Fairfax Media revealed leaked departmental modelling on Sunday showing Catholic schools would be $4.6 billion worse off over a decade under Gonski 2.0 than under current arrangements, with $4 billion extra flowing to public schools over the same period.

Ahead of a potentially fiery party room meeting on Tuesday, former cabinet minister Kevin Andrews demanded Education Minister Simon Birmingham release the data to his colleagues.

Mr Andrews said he would struggle to vote for any deal with the Greens that left Catholic schools worse off.

"The modelling has not been provided to the party room - I hope it will be provided tomorrow," he said.

Asked if he could cross the floor when an amended bill returns to the House of Representatives, Mr Andrews said: "I won't get ahead of myself but I will be surprised if it [the modelling] is not provided to us.

"Then people can see what the data shows and make up their own minds."

Another MP said Senator Birmingham had made a "major mistake" by providing the data to the Senate crossbench but not the Coalition party room.

And another MP said simply: "This won't get through the party room unless the Catholics are happy. Why should a poor Catholic parish school get less money than a public school?"

Senator Back, who will retire from politics this week, said: "Until I'm convinced that the proposals in place will not disadvantage Catholic schools, and independent schools for that matter, I've indicated to the minister: 'please don't make me vote against the government in my last week in the Senate'."

Senator Birmingham said Catholic school funding would rise by 3.5 per cent annually per student over the next decade under the government's changes.

In question time on Monday, Prime Minister Malcolm Turnbull accused Labor of "hypocrisy" and "political gamesmanship" for opposing the new model.

"Every system - state, territory, Catholic, independent - is getting more funding per student across the board based on need," he said.

Fairfax Media understands the government is willing to offer a review of the socio-economic status methodology underlying its funding model to help appease MPs worried about the impact on Catholic schools.

But anything that could be described as a "special deal" for the sector was not possible, sources said.

Coalition MPs have been receiving intense resistance from Catholic school parents in their electorates over the changes.

Sydney Liberal MP Paul Fletcher was heckled by Catholic parents at a fiery meeting attended by about 500 of his constituents on the weekend.

Sources who attended the meeting said some parents, concerned about massive fee rises, were in tears and said they would have to send their children to a public school if the changes passed.

Despite the potential of a deal with the party, audio of the meeting shows Mr Fletcher repeatedly telling parents: "the Greens are not your friend".

Catholic Education Commission of Victoria boss Stephen Elder said the Catholic sector was prepared to campaign against high profile Liberal MPs at the next election if they vote for the new model.

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