The Allan government has rejected an order from the upper house to release former Victoria Police boss Ken Lay's report into a possible second injecting room by Wednesday.

In a response to the motion, Attorney-General Jaclyn Symes claimed the document was subject to executive privilege.

"Whilst a claim of executive privilege is made at this time, the government stands by its commitment to release the report alongside the government's response to the report," she said in a letter tabled on Wednesday.

Executive privilege can allow governments to withhold information from the legislature on public interest grounds.

The report, which was commissioned back in 2020, maps out drug-taking patterns in the Melbourne CBD and will provide advice on establishing a medically supervised injecting service trial in the city.

It was handed to the state government at the end of May but remains unpublished.

Premier Jacinta Allan reiterated the Lay report would be released this year and refused to say whether the government was reconsidering its position to set up an injecting room somewhere in the CBD.

"We're considering the advice," she said.

Opposition Leader John Pesutto said the government had shown contempt for parliament and disputed its executive privilege claim, pointing to the commitment to release the report once it finalises a response.

"It's an issue that is causing enormous uncertainty around our CBD and surrounding suburbs," he said.

"People want to know what's in this report."

The opposition will move another motion next sitting week demanding Ms Symes provide a copy of the report to an independent arbiter to rule on whether the executive privilege claim is justified.

A medically supervised injecting room trial in the CBD has been mooted for years, with the government buying a building near Degraves Street and a Salvation Army hub on Bourke Street flagged as a potential site in July.

Victoria's first injecting room in North Richmond was opened in June 2018 under a trial and made permanent in May after a review found it safely managed almost 6000 overdoses and saved 63 lives.

Victorian Alcohol and Drug Association chief executive Chris Christoforou said the need for a second injecting room was critical to addressing continuing drug-related harms in the CBD.

"We are encouraged by comments this morning of the need for an enhanced drug surveillance system and other harm reduction initiatives in response to a changing drug market and the risk of potent synthetic opioids such as fentanyl," he said.

"The risks around such substances wreaking havoc in our community is a conversation Victoria has to have."

Australian Associated Press