Debate on doomed plebiscite begins

Debate on legislation to establish a plebiscite, which is expected to fail without Labor's support, has kicked off.

Debate on legislation for a plebiscite, expected to fail without Labor's support, has kicked off. (AAP)

Federal Labor is using plebiscite legislation to urge the parliament to withdraw the bill and redraft it to legalise same-sex marriage.

Politicians began debating the doomed plebiscite bill on Tuesday after Labor officially confirmed it would oppose the national same-sex marriage vote.

Without crossbench support in the Senate, the government plan will almost certainly fail.

Speaking against the bill, Opposition Leader Bill Shorten moved a second reading speech amendment stating: "this bill be withdrawn and redrafted to legislate for marriage equality".

It went on to add: "that the House calls on the government to afford all members of parliament a free vote."

Mr Shorten believes the plebiscite is expensive, unnecessary and damaging to gay Australians.

"Let's get on with it and make marriage equality a reality," he told parliament.

"Equality for minorities should not be conditional on the opinion of the majority."

Liberal MP Warren Entsch - a staunch supporter of same-sex marriage - believes some people are losing sight of the end game while focusing on the battle.

"This is the never never unless we start to deal with this issue now," he told those saying only a free vote could bring on same-sex marriage.