The ‘Yes’ campaign has ramped up efforts for the same-sex marriage postal survey, with its methods including a controversial text message blast to voters across the country.

Same-sex marriage supporters launched a national doorknocking campaign at the weekend, but some Australians were unhappy about receiving unsolicited ‘Yes’ camp text messages.

The messages read: “The Marriage Equality Survey forms have arrived! Help make history and vote YES for a fairer Australia. VoteYes.org.au.”

The ‘Yes’ campaign confirmed the messages were sent to random computer-generated phone numbers, with some voters complaining they were “rude” and an “invasion of privacy”.

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As the postal survey is non-compulsory, many observers believe the result will hinge on voter turnout, though experts said tactics such as unsolicited messaged risked a backlash from voters.

Privacy expert Anna Johnston said “spamming is a surefire way to get the undecideds to distrust your campaign like they distrust politicians”.

She said “direct [communications] should be opt-in only” because the community’s expectations were set at a “higher standard than the law”.

Prominent communications guru Dee Madigan said: “Whoever thought sending texts from a randomly generated list was good campaign strategy is not a good campaign strategist.”

But the ‘Yes’ camp defended the move, with co-chair Alex Greenwich saying it was “using every resource available to make sure fairness and equality are achieved for all Australians”.

‘No’ voter George Christensen said he’d received complaints about the text messages. Photo: AAP

“The campaign has a responsibility to encourage every Australian to post their survey and we have done this through doorknocking, media, advertising, social media and SMS messaging,” he said.

Deputy Opposition Leader Tanya Plibersek, who is campaigning for a ‘Yes’ vote, said the complaints were “ridiculous”.

“We didn’t want this postal survey to happen,” she told the ABC.

“We’ve said all along that this is $122 million waste of money that is very distressing for a lot of people.

“And then, when the ‘Yes’ campaign actually goes out and campaigns, as you would in a general election, the ‘No’ campaign [is] saying that it is unfair that people are urging a ‘Yes’ vote. It’s ridiculous.”

Nationals MP George Christensen said he had received “numerous complaints … about text messages being sent from those seeking to change the definition of marriage”.

Receiving a lot of feedback from people unhappy about getting unsolicited texts from the 🏳️‍🌈 Yes Campaign.

— Lyle Shelton (@LyleShelton) September 23, 2017

The ‘Yes’ campaign’s increased outreach follows polling that has shown support for a change in the law has fallen, though it remains the most likely result.

Ms Plibersek said on Sunday that the “biggest risk” for ‘Yes’ campaign was “apathy”.

“The biggest threat to the ‘Yes’ campaign’s success is people assuming that this is in the bag because they know that a majority of Australians support marriage equality, and they think, ‘Oh well, my vote won’t matter, you know, everybody else will post back their ‘Yes’ vote’,” she said.

‘No’ campaigners last week seized on the alleged assault of former prime minister Tony Abbott in Hobart by a man wearing a ‘Yes’ badge.

Mr Abbott suggested “the love is love brigade isn’t showing a lot of love”, though the alleged offender, self-described anarchist Astro Labe, has since said he was not motivated by the issue.

Same-sex marriage advocates have pointed to incidents of violence and abuse directed at ‘Yes’ supporters, including the alleged assault of Kevin Rudd’s godson, Sean Foster, in Brisbane, earlier in the month.

Meanwhile, the government lost another percentage point in the latest Newspoll, bringing its support to 46 per cent against Labor’s 54 per cent on two party terms. It was the 20th consecutive Newspoll in which the Coalition had trailed Labor.

Prime Minister Malcolm Turnbull also gave up four percentage points of his lead (42) as preferred prime minister, with Labor leader Bill Shorten narrowing the gap by two points (31).