Labor has relied only on advice from the government solicitor to back its claim that the election period has not officially begun, Communication Minister Stephen Conroy says.

Prime Minister Julia Gillard's unprecedented early announcement that the federal poll would be on September 14 sparked debate about whether the "election period", which triggers special broadcasting rules, had begun.

The Australian Communications and Media Authority says it hasn't.

But it's been reported that some commercial television stations have legal advice that say the special provisions of the Broadcasting Services Act have been triggered.

Broadcasters are required to vet any political advertising and ensure balance in any coverage under those rules.

Opposition backbencher Simon Birmingham asked Senator Conroy during a Senate estimates hearing on Tuesday if the government had sought legal advice from anyone other than the government solicitor.

"No, I don't believe so," Senator Conroy said.

He said the government would not release the advice publicly.

Communications Department secretary Peter Harris said the department's view was that the election period began when the writs were issued - on August 12.

Comment was being sought from Free TV, the commercial networks' peak body.