The Liberals want Canada's information commissioner to investigate Stephen Harper's office and the minister of natural resources over meddling in access-to-information requests.
Last week, an aide to Natural Resources Minister Christian Paradis resigned after documents obtained by The Canadian Press showed he interfered in at least four requests, not just the one he had admitted to.
Now the Liberals say Information Commissioner Suzanne Legault should expand her probe to include Mr. Paradis and the PMO.
In a letter to the commissioner sent Sunday, Liberal MP Siobhan Coady said the interference from the minister's office was well documented.
But Ms. Coady said there was also reason to look into what role, if any, Mr. Harper's staff played.
She said there had been reports in the media that Mr. Harper's staff wanted ministerial staff to head off releases of sensitive material.
"I ask that your investigation include an examination of involvement by the Prime Minister and his office," she writes.
"The investigation may uncover similar examples of interference in other departments."
Under Canada's Access to Information Act, it is forbidden to "destroy, mutilate or alter a record, falsify a record ... (or) direct, propose, counsel or cause any person in any manner to do (so)."
The aide, Sebastien Togneri, who resigned Thursday, was already being investigated over his blocking of one access-to-information request while Mr. Paradis was at Public Works.
He continued to work for Mr. Paradis after the minister moved to Natural Resources.
Mr. Paradis said last week he had requested that the information commissioner investigate Mr. Togneri.
Mr. Harper's chief of staff issued a memo in February, reminding all political staff in ministers' offices of the law's requirements.
"No political staff member has received a delegation of authority under the Act and therefore no political staff member has authority to make access-to-information decisions," Guy Giorno wrote.