Opposition Leader Bill Shorten has told Prime Minister Malcolm Turnbull that Labor will blame him for the "filth" that will be aimed at gay people as debate rages on over changing the marriage laws.

"I hold you responsible for every hurtful bit of filth that this debate will unleash," Mr Shorten said in a fiery speech in Parliament this afternoon.

He spelled out that Labor would campaign for a Yes vote in the postal ballot, despite arguing the process was unnecessary and would leave gay people open to vilification.

"We say to young Australians who are gay, we are voting in this survey because of you, not because we respect the process, but because the Labor Party will not let gay Australians and young gay people cope with this survey, this evaluation of their relationships, on their own," he said.

But he attacked the process as a "ridiculous waste of time and taxpayer money", saying the $122 million would be better spent on dialysis machines, teachers, housing or training.

Mr Shorten accused Mr Turnbull of spending the $122 million to try to save his own job.

He said extremists were already using the debate to smear same-sex couples and their children.

"Every hateful ideological hobby horse will be saddled up for this vote and it is clear who is responsible," Mr Shorten said.

"In less than 48 hours the Prime Minister has gone from promising to call out extreme voices to saying they are entitled to their view."

He also slammed the process that had been laid out for running the ballot, in particular because voters would not know the exact wording of the legislation that would be enacted if they approved a change.

Mr Shorten was highly critical that normal electoral rules would not apply and there would be "no protection against ballot fraud, electoral bribery, intimidation, interfering with the electoral roll, publishing misleading and deceptive material".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 minutes 2 seconds 6 m Supporters of same-sex marriage divided over postal vote

Labor 'constantly delayed, stalled, opposed change'

Liberal MP Tim Wilson hit back at Mr Shorten, pointing out that Labor did not legislate for same-sex marriage when it was in government from 2007 until 2013.

Mr Wilson told Parliament it had meant he had not been able to get married to his partner.

"As the only member of this House who is actually engaged to their partner of the same sex, for seven years I have been engaged," he said, "mostly during the time of the previous and current government".

He accused many in Labor of moral posturing and said they had "constantly delayed, stalled, blocked and opposed change" before changing their opinion.

"Taking a lecture about the failure to pass a law from the Opposition is a bit rich," Mr Wilson said.

"They had the potential for so many years to deliver this, it was immensely frustrating to watch that they did not.

"First we had Kevin Rudd who opposed it on religious grounds, then we had Julia Gillard who opposed it on feminist grounds, then we had Kevin Rudd who was for it and did not act."

The Public Interest Advocacy Centre has asked the High Court to decide if the Government has the power to order a postal vote on same-sex marriage.

Voluntary postal ballots will be sent out to voters from next month.

The Centre argued the Government may have exceeded its executive powers by ordering the vote without passing legislation.

It said it may not be legal for the Australian Bureau of Statistics to run a vote — instead of just collecting information.