The Turnbull government's hopes it can pass its landmark "super savers" scheme for first home buyers this year appear all but dashed.
The legislation for the scheme, set to be introduced on Monday, will require the support of all but two crossbench senators.
Treasurer Scott Morrison drew attention to the plight of the scheme on Wednesday amid questions about the ongoing citizenship fiasco.
"If you're saving right now for your first home, then you are far more interested in making sure the Parliament legislates to give you a tax cut on your first home savings than who my parents are or anyone else's parents are and I think that gives the issue some focus," he said, adding the government had "been working constructively with the crossbench".
But crossbench senator Jacqui Lambie told Fairfax Media she had ongoing "concerns" about the legislation while Cory Bernardi and David Leyonhjelm declared the proposal would do nothing to help first home buyers, almost ensuring the May budget proposal will not pass before next year.
Four new senators will be sworn in on Monday, including Liberal Hollie Hughes, the replacement for NSW National Fiona Nash, and 22-year-old Jordon Steele-John, who will take the place of WA Green Scott Ludlam.
The appointments mean the number of vacancies in the Senate will drop from six to two, with Labor agreeing to pair outgoing senators Nick Xenophon and Liberal Stephen Parry.
In a sign of how keen the Turnbull government is to get the legislation moving, the new senators will face the first home super saver scheme as one of the first matters of business on Monday.
Here it will begin a tortuous path through the Senate, where the government will have to secure the votes of the Nick Xenophon Team and One Nation as part of the 10 crossbench votes it needs to pass into legislation without the support of Labor or the Greens.
The scheme was designed to allow people to save up to $30,000 in voluntary tax-exempt super contributions that they can draw on when buying their first home.
Labor and the Greens have vehemently opposed the proposal, arguing it would increase prices and add existing pressure in the housing market while failing to remove negative gearing and capital gains tax concessions.
When it was first announced, Senator Bernardi described the scheme as a terrible policy dressed up as a tax cut and said on Wednesday his position had not changed.
Senator Leyonhjelm, a libertarian, said he was against any federal government intervention in the housing market and that any negotiation would be delayed until next year by the same-sex marriage survey result on Wednesday.
"We are in favour of using our superannuation savings to account for more than just superannuation as a tax advantage," he said.
"But allowing superannuation to be used for housing is unlikely to solve the housing affordability problem, it will just push prices up."
Senator Leyonhjelm said he would seek an unlikely deal with the government to allow super to be accessed for health insurance and education.
The Nick Xenophon Team has indicated it will support the proposal while a spokesman for One Nation said it had held "party discussions" but was yet to arrive at a position.