The government’s proposed marriage plebiscite has been delivered a fresh blow with openly gay Liberal senator Dean Smith declaring he will not vote for it.

Smith, from Western Australia, said the notion of sidelining parliament through “people’s votes” was “abhorrent to constitutional conservatives”, and foreshadowed he would cross the floor or abstain from voting on the legislation.

In an article for Fairfax Media, he indicated his stand was on the basis of his commitment to representative democracy rather than driven by his sexuality. The plebiscite would set a dangerous precedent for deciding other controversial issues on the basis of popular votes, he said.

“As a lifelong conservative, I am not prepared to see the principle of parliamentary sovereignty undermined for all time, simply because in this moment, it is politically convenient,” he wrote.

He informed the Coalition partyroom of his position when it considered the plebiscite on Tuesday morning.

The plebiscite increasingly appears doomed when the legislation reaches the Senate, with Opposition Leader Bill Shorten again trenchantly attacking it and Labor homing in with critical questions in parliament.

Attorney-General George Brandis and Special Minister of State Scott Ryan outlined the shape of the vote at a news conference after the party meeting. Legislation for it will be introduced this week. The proposed date for the plebiscite is February 11.

The question would be: “Should the law be changed to allow same-sex couples to marry?” Brandis said this was a completely neutral formulation. If the plebiscite was passed he would immediately introduce enabling legislation to implement the result.

Ryan said the result would be decided by a simple majority. Voting would be compulsory. Material would have to be authorised, as in elections. The government would also be seeking to have authorisation apply to “new communications mechanisms such as robocalls and SMS messaging”.

This follows the election experience of Labor’s text messages about Medicare – denounced by the government – as well as a massive phone campaign by the ALP.

Ryan said there would be “yes” and “no” advertising committees established, based on the precedent of the 1999 republic referendum. The government would provide A$7.5 million to each of the “yes” and “no” committees.

Each committee would have ten members, including five members of parliament, two from the government, one from the crossbench and two provided by the opposition. The other five on each committee would be appointed by the government, again following the republic referendum experience.

The question of public funding has been divisive within the government. In the Coalition partyroom there was some argument on that issue, with one speaker challenging the spending of public funds when the question being put was a simple one.

Brandis called on Shorten “to get out of the way, to allow the plebiscite bill passage through the Senate, to allow the Australian people to have their say and, importantly, in the event that there is a yes vote in the plebiscite to allow there to be marriage equality in Australia by early next year”.

Shorten said he was surprised Turnbull had “given in to the bullies so much that now he’s gone down the slippery slope of spending taxpayer money to fund an opinion poll which most Australians don’t see the point of”.

He said Labor would be talking further to people who would be affected by this vote and to mental health experts. “But we have grave reservations. Is the emotional torment of people worth it? Is it worth $160 million plus $15 million, plus whatever else gets spent? Especially when it’s not binding upon government MPs.”

In Question Time Deputy Opposition Leader Tanya Plibersek said in a question to Turnbull: “This morning I met 13-year-old Eddie, who is visiting Canberra today with his two mums, asking parliament to block a plebiscite. He said to me and I quote, ‘Why should people who barely know us make an assumption on our families and vote on how we can live?’ Can the prime minister explain why Eddie should have to put up with a $7.5 million campaign, by people who have never met him, telling him that there is something wrong with his family?”

She said Eddie was watching from the public gallery. Turnbull said he was “very disappointed” she would take advantage of Eddie’s presence in this way.

Greens senator Sarah Hanson-Young, who had kept her options open on how she would vote on the legislation to establish the plebiscite, said that now she had seen the proposal she would not be supporting it.

“Malcolm Turnbull has forsaken the marriage equality movement and allowed for this plebiscite to be rigged, so that it will never see the light of day. I could never accept spending taxpayers’ money on a campaign that attacks members of the Australian community,” she said.

The Greens declared some time ago they would oppose the legislation to set up the plebiscite.