The federal government's deficit levy has passed the Senate despite dissent in Coalition ranks over the temporary tax.
The 2 per cent tax on individuals on incomes over $180,000 or more is the first in a series of controversial budget measures to be considered by the Senate and passed comfortably on Tuesday with Labor's support.
'It just doesn't make sense to me': Coalition senator slams deficit levy
LNP senator Ian Macdonald says the deficit levy should apply to businesses as well as individuals, and that the Government's paid parental leave scheme should be scrapped.
The measure was passed on voices, meaning it was not put to an actual vote and dissent from government senators Ian Macdonald and Cory Bernardi could not be recorded in the vote.
But Senator Macdonald again used debate on the issue to pressure his own party over the tax, which he says does not go far enough and should also be imposed on companies.
He reiterated comments he made on Monday, when he threatened to cross the floor on a number of government policies, saying he could not understand "why individuals are being requested to make the contribution but not companies".
Senator Macdonald on Tuesday pressured Finance Minister Mathias Cormann, demanding to know why companies "aren't being asked to pay off Labor's debt?"
Senator Cormann said everyone was being asked to do their bit in the budget, a response that Senator Macdonald said failed to convince him of the levy's merits.
The government will have a tougher time finding support for other budget measures, including its $7 GP fee and Prime Minister Tony Abbott's paid parental leave scheme.
The government is deeply divided over paid parental leave, with Senator Macdonald among a group of Coalition MPs who have spoken out against the generous scheme.
Senators John Williams, Ron Boswell and Cory Bernardi have also indicated they are unhappy with the proposal.
Labor has seized on the dissent, particularly from government MPs in regional seats.
Shadow treasurer Chris Bowen has written to Nationals MPs urging them to drop public support for the scheme and work with the opposition to defeat it.
In letters to Deputy Prime Minister Warren Truss and deputy Nationals leader Barnaby Joyce, Mr Bowen said: "If you are serious about supporting regional Australia, I urge you to join with the Labor Party and oppose the Liberals' Paid Parental Leave scheme and the unfair Budget cuts to that will hit regional Australians the hardest."