The union representing journalists has criticised George Brandis’s announcement that prosecution of journalists under the government’s new national security laws would have to be cleared by the attorney general.

Paul Murphy, the director of media at the Media, Entertainment and Arts Alliance (MEAA), has told Guardian Australia “it gives us no comfort at all that politicians will sit and decide” who goes to jail under the laws.

Section 35P of the new national security legislation, which cleared both houses of parliament last month, states that the publishing of special intelligence operations (SIOs) information can be punishable by up to 10 years’ jail. The government can deem which operations can be defined as an SIO.

Civil Liberties Australia expressed its opposition to Brandis’s oversight provisions.

“Changing the ultimate decision-maker might advance political ends, but it is no extra or comforting protection for journalists or the Australian people. In fact, cynics would think such a proviso was capable of being used to threaten to prosecute a journalist so as to “encourage” them to reveal their source,” it said.

The opposition leader, Bill Shorten, said Brandis’s decision to become “a sort of last sentinel on the wall of press freedom” was not satisfactory.

Greens senator Scott Ludlam said the provisions amounted to the “politicisation of national security”. He said the focus on journalists under 35P was a “remarkable deception” by Brandis, as the laws could apply to anyone.

“There are no protections for whistleblowers under this legislation, and that’s no accident. It’s designed that way,” Ludlam said. He said Australians may unwittingly find themselves on the wrong side of the law.

“Sharing a Facebook post on a national security story is enough to see you prosecuted,” Ludlam said. “It’s clear that 35P will be used to prosecute people,” Murphy said. “If not journalists, then whistleblowers and sources.”

He said the fact that Brandis mentioned American whistleblower Edward Snowden in the press conference he held on Thursday was “quite telling”.

Brandis said in that press conference that the prosecution of journalists was a “barely imaginable event”, and that 35P was “intended to deal with a ‘Snowden’ type situation.

“There is no possibility, no practical or foreseeable possibility, that in our liberal democracy a journalist would ever be prosecuted for doing their job,” Brandis said on Thursday.

“The prosecution can only be brought by the director of public prosecutions but this would add a very powerful safeguard by providing that the attorney general would be required to consent to and therefore accept personal and political responsibility for a prosecution, in the barely imaginable event that such a prosecution were brought.”

Shorten had a change of heart about the national security laws after the legislation was passed, saying Labor has “concerns” about the powers contained within 35P. He’s calling on the government to implement a review of the legislation, undertaken by the national security legislation monitor (NSLM), by the end of June.

The government had proposed to scrap the NSLM earlier in the year, but reversed the decision in August in light of national security changes.