NSW would become the first Australian state to expressly curb the use of "gay conversion" therapies for children but it would remain legal for consenting adults, under a compromise proposal for a debate threatening to split Labor.

A motion, sponsored by the left-wing Australian Manufacturing Workers Union, for next weekend's state Labor conference would criminalise "any attempts to convince someone to change their sexuality by any means".

Mr Secord says he personally opposes such therapies but only wants to their use on children curbed. Credit:Andrew Taylor

The party's platform, debated at its annual conference, already condemns "ex-gay therapy", but some left proponents have warned further moves could provoke ire from Labor's conservative unions and factions.

But the party's shadow health minister, Walt Secord, from the right, will instead suggest a consensus plan that would have the state's Attorney-General and Health departments investigate curbing any therapies involving children under 18.