Monday looms as D-Day for the Turnbull government's precarious plebiscite on same-sex marriage, with the Coalition and Labor to sit down in Brisbane for talks.

Attorney-General George Brandis and Special Minister of State Scott Ryan will meet with shadow attorney-general Mark Dreyfus in a last-ditch attempt to find a compromise that might win Labor's crucial support in the Senate. It precedes a cabinet meeting in Canberra on Monday night.

But any genuine attempt at negotiation appears doomed from the start, with Labor making demands to which the Coalition will find it impossible to accede.

Mr Dreyfus on Friday mentioned two changes - dumping public funding for both sides' campaigns, and making the plebiscite self-executing or binding - as necessary but not sufficient for Labor to reconsider its position on the issue.