Greens senator Sarah Hanson-Young moved to establish a parliamentary inquiry into legislation aimed at banning gambling ads.
She said she expected both Labor and the Liberals to oppose the move, accusing Labor of failing to act on the Peta Murphy report into gambling advertising.
Following the Coalition split, Nationals senator Matt Canavan confirmed the Nationals would support the inquiry.
Canavan said the Greens often went too far on bans but argued parliamentary scrutiny of gambling advertising was justified.
As the Senate division commenced, Nationals senators sat with the Greens and independent David Pocock, while Labor and Liberal senators voted together against the inquiry.
Despite support from the Greens, the Nationals and independents, the proposed Senate inquiry into gambling advertising was defeated 29 votes to 19, with Labor and the Liberals voting together to block it.
Less than an hour later, Labor and the Liberals again voted together to block a second inquiry motion moved by Hanson-Young, this time seeking broader scrutiny of the harms caused by gambling advertising.
Hanson-Young criticised the repeat vote, accusing the major parties of shutting down parliamentary scrutiny for a second time in the same sitting.
