Treasurer Joe Hockey says the critics of the PPL scheme are trying to stop the Coalition keeping its election promise.

Treasurer Joe Hockey has urged his Coalition colleagues "not to fall" for the "class-war rhetoric" of the Labor Party in relation to the Government's new paid parental leave scheme.

The scheme, which would replace a woman's wage for six months, up to a cap of $50,000, has been criticised by some Coalition MPs.

There are reports today that the Prime Minister has been told enough Nationals and Liberal MPs would cross the floor to ensure the scheme was defeated in the Senate.

But Mr Hockey has given no sign the Government is being forced to back away from the scheme, saying the reports are not correct.

He added that the draft legislation is "not too far away" and is likely to be introduced to Parliament this year because "it is meant to start next year".

The Treasurer emphasised that farmers, their wives, small business owners and women on low and middle incomes would benefit from the new payments.

"We have laid down our plans for the paid parental leave scheme. We have taken it to two elections," he said.

"I just say to the critics, you want us to keep our election promises, now you're doing everything you can to stop us keeping our election promises. So please make up your minds.

Parental leave scheme The scheme will provide mothers with 26 weeks of paid parental leave at their actual wage or the national minimum wage (whichever is greater), plus superannuation.

The Coalition went to the election saying a woman earning $150,000 or more would receive the maximum cap of $75,000, but dropped the threshold to $100,000 with a maximum payment of $50,000.

From July the minimum wage will be $640.90 per week. At this rate, the minimum paid parental leave payment would be $16,663.40.

The current paid parental leave scheme, set up by Labor, pays all eligible mothers the minimum wage (currently $622.10) for a maximum of 18 weeks, totalling just over $11,000.

"Can we just get away from the class-war rhetoric of Labor and I would urge my colleagues not to fall for the class-war rhetoric of the Labor Party and the critics and focus on who will benefit and how they will benefit."

Deputy Prime Minister and Nationals leader Warren Truss has noted the criticism has come from both Nationals and Liberal MPs, but he is standing by the scheme.

"From my perspective this is Coalition policy, it has been discussed in the Nationals party room on a number of occasions, we support it because it is Coalition policy," he said.

"I think that the scheme offers enormous benefits for poorer Australians, particularly those in regional communities and those in small business."

Mr Abbott has already cut back the maximum payment for his signature scheme, dropping it six weeks ago from $75,000 to $50,000 over six months.

Labor has criticised the plan as a "Rolls Royce" scheme that gives "money to millionaires" and it is also opposed by Senate crossbenchers Nick Xenophon, John Madigan and new Senators Family First Bob Day and Liberal Democrat David Lejonhjelm.

The key crossbench party in the new Senate, the Palmer United Party, is also opposed to the scheme.

The Greens are withholding support but have indicated they would be open to negotiations.

Greens leader Christine Milne says she is waiting to see the model the Government puts to Parliament.

"We want a scheme which is fully paid for by big business. We don't want a dollar coming out of the public purse. That is on the table," she said.

"We don't know where Tony Abbott's thinking is and clearly he hasn't got his own side under control let alone the parliament."

It puts in play the votes of Coalition MPs who may oppose the scheme and be willing to cross the floor.

The PPL scheme would cost the budget $5.5 billion per year, partly funded by a 1.5 per cent tax increase for big companies.

Mr Abbott announced the policy while in Opposition after attending an International Women's Day lunch, without consulting his shadow cabinet or party room.

The current government-funded scheme, which was introduced by Labor in 2011, pays women the minimum wage for 18 weeks.

The Senate is also proving troublesome for the Government on several key budget measures, such as the $7 fee on GP visits, x-rays and blood tests, changes to pensions and - possibly - family benefits.

Mr Hockey is taking a tough line, warning that an oppositionist Senate may force the Government to take the nation back to the polls.

"If [the Senate] just continually says no without any capacity to negotiate, an improved outcome that is, the Senate becomes irrelevant," he said.

"It is just simply a road block and we either have to smash through that road block or the Australian people get the chance to change Government."