Bill Shorten wants Malcolm Turnbull to publicly release the next coalition agreement between the Liberals and the Nationals and ensure it includes the power to sack the deputy prime minister.
Mr Turnbull was unable to fire Barnaby Joyce as deputy prime minister despite a damaging scandal because only Nationals MPs could choose to replace their boss.
"The government's first priority here must be to make sure we never see a situation where the prime minister is emasculated to the point he can have no say in the deputy prime minister," Mr Shorten told reporters in Melbourne on Friday.
The next Nationals leader, to be decided on Monday, will need to exchange letters with the prime minister committing to a new coalition agreement.
Former attorney-general George Brandis last year described the coalition agreement as a "private document ... exchanged between two individuals in their capacity as leaders of two political parties, not as public office holders".
Labor has unsuccessfully sought the release of previous agreements in court.
"The Nationals cannot be allowed, by virtue of a secret coalition agreement, to 100 per cent decide who the deputy prime minister is," Mr Shorten said.
Greens leader Richard Di Natale said Mr Turnbull had been "powerless" to sack Mr Joyce
"That is because he is a signatory to a secret agreement that never should have been made secret," Senator Di Natale told reporters.
It is understood the agreement sets out priority policy areas, proposed major projects of interest to regional and rural areas, which portfolios the Nationals want on the frontbench and that the Nationals leader will be deputy prime minister.
