Conservative senator Cory Bernardi has defended targeting millions of homes with robo-calls urging people to vote 'no' in the same-sex marriage postal survey.

But he has simultaneously attacked as an invasion of privacy bulk text messages sent out by marriage equality advocates urging Australians to vote 'yes'.

"Taking the poll of an electorate or doing some market research is a time-honoured political technique and that's exactly what we're doing," Senator Bernardi told Sky News on Thursday.

"This is just polling an electorate - it's stock in trade of any political business - and it's not invasive like sending text messages to unlisted numbers or to 12-year-olds telling them how to vote."

In a copy of the phone call recording published by Nine News, the senator tells households in Victoria and South Australia that same-sex marriage is a recipe for division.

He goes on to add that it would remove gender from all areas of society including schools.

"As a parent, I am deeply concerned about how changing the marriage act will affect families and children," he says.

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"Ultimately this is a question about parents' rights."

Senator Bernardi then outlines concerns about "radical gay sex education" and gender ideology programs before asking people to indicate how they'll vote in the survey by using their keypads.

"For some reason people feel that their mobiles are more personal space," he said of the apparent distinction between the unsolicited calls and text messages.

"To have randomly generated numbers and have people targeting or telling you what to do through that seems to have upset a great many people."