The Federal Opposition says it will not block the Coalition's proposed debt levy for those earning more than $180,000 a year.

Labor's leader in the Senate, Penny Wong, told the ABC's Insiders program that the Opposition would "not stand in the way of that levy".

"We'll vote for it if that's what's required in the Senate," she said.

"Obviously ultimately it's a matter for the cross benches as well as to whether or not that will be needed, but we won't be standing in the way."

Senator Wong said the Opposition was prioritising which budget measures items to fight, and a tax increase on high-income earners was not a priority.

However, she said Labor remained firmly against changes to welfare and Medicare.

She also ruled out negotiating with the Coalition on plans to deregulate universities, despite signals from Education Minister Christopher Pyne that the Coalition was willing to negotiate.

"I'm not going to respond to Christopher Pyne's latest thought bubble," she said.

"Let's be clear on what he's proposing in relation to higher education. He's proposing a set of changes which will put out of reach of many Australians a university education."

The Greens have also warned the Government that the Senate will not cave in to passing the budget unamended.

Greens leader Christine Milne says Prime Minister Tony Abbott cannot "ram" the budget through.

"He is going to have to understand that the Australian people did not give him control of both houses of Parliament for good reason and the Senate is not going to cave in to him," she said.

Hockey dismisses broken promise suggestion

Meanwhile, Treasurer Joe Hockey says it is "ridiculous" to suggest governments will never raise taxes.

The Coalition has come under criticism for its proposed deficit levy, a GP co-payment and increases to the fuel excise.

That is despite Mr Abbott promising before the election that there would be no new taxes under a Coalition government.

However, Mr Hockey has rejected on Sky News that the Coalition had broken an election promise.

"No, because the suggestion we were never going to increase a tax is ridiculous," he said.

"No government never pledges to never increase any tax at any point. What matters is the overall tax intake."