Labor frontbenchers say they will keep pushing to question the Government on why incorrect evidence about the Lindt cafe gunman was given to a Senate committee.

The evidence related to a letter Sydney siege gunman Man Haron Monis sent to Attorney-General George Brandis last year.

The official told a hearing last week the letter and the response from the department were both scrutinised by the joint Commonwealth-New South Wales review of the tragedy, but that never happened.

Labor wants to urgently recall Senate estimates as soon as next week to find out what went wrong.

To do so, three committee members need to request an extra hearing.

Shadow attorney-general Mark Dreyfus said he would discuss the issue with the Labor senators on the committee.

"I'd expect the Government to cooperate because the Government's got some questions to answer," he said.

"The Government needs to clear this up, it's raised some real concerns. And we were right to raise concerns last week.

"It's quite disturbing to now see that the centrepiece of the Government's intemperate attack on me and on Labor last week, which was the assertion that the letters had been given to the inquiry, has proved to be completely false."

Labor has also accused the Government of sitting on the information about the false evidence until after Question Time wrapped up for the week, when Foreign Minister Julie Bishop advised the Parliament.

"My statement was based on the evidence given by the deputy secretary of the Attorney-General's department, Ms Katherine Jones, in budget estimates," Ms Bishop told Parliament.

"The Attorney-General's department has now advised that Ms Jones' evidence was incorrect."

Senator Brandis said in a statement he was told on Monday the evidence given to estimates about the letters "appeared" to be wrong.

But the statement said this was not confirmed until yesterday afternoon, and he acted immediately to correct the record.

Mr Dreyfus said Senator Brandis took too long to act.

"Senator Brandis has got some serious questions to answer and that's why we're recalling the Senate estimates," he said.