Federal lawyers are using the anti-terrorism law to bully a diplomat who planned to testify about prisoners risking torture when Canadian troops hand them to Afghan officials, his attorney alleges in a letter obtained by The Globe and Mail.

Richard Colvin had been subpoenaed before a public inquiry into the treatment of Afghan detainees, which resumes hearings Wednesday.

Held by the Military Police Complaints Commission, the inquiry is probing whether Canada failed its duties under the Geneva conventions to ensure prisoners aren't abused.

However, Ottawa is trying to stop Mr. Colvin and several other witnesses from testifying, citing concerns about national security.

The move is part of a string of roadblocks raised by federal lawyers that have delayed and severely limited the scope of the inquiry.

Mr. Colvin's feelings or those of his lawyer, Lori Bokenfohr, weren't public until now.

In a letter sent Monday to her federal counterpart, Alain Préfontaine, Ms. Bokenfohr complained that he misused sections of the Anti-Terrorism Act to muzzle her client.

“The legislation was addressed at combatting terrorism-related activities. It was not intended to be used tactically to intimidate witnesses from giving evidence in administrative proceedings carried out by government-created bodies,” the letter said. “The interests of justice are not served when an ordinary witness such as Mr. Colvin is threatened by the Department of Justice with severe penalty for abiding by the terms of a subpoena served on him.”

Ms. Bokenfohr didn't provide the letter to The Globe. She confirmed its existence but wouldn't comment further.

The Anti-Terrorism Act – which amended a series of laws, including the Canada Evidence Act – was adopted after the attacks of Sept. 11, 2001.

Ottawa lawyers invoked Section 38 of the Canada Evidence Act to tell the inquiry that the evidence it will hear is so sensitive that key witnesses should be excluded.

The government also wants the remaining witnesses to take questions in writing only, with transcripts of their answers to be edited by federal lawyers before they are released to the inquiry.

In her letter, Ms. Bokenfohr said that Ottawa is in a conflict of interest since its lawyers want to vet all evidence and at the same time counsel the military police officers who are the subjects of the inquiry.

Mr. Colvin now works at the embassy in Washington as deputy head of the Intelligence Liaison Office. He was political director of the Kandahar provincial reconstruction team until 2007.

In a previous letter, Ms. Bokenfohr said Mr. Colvin has personal knowledge of what the military police knew about the risks of torture.

Other correspondence obtain by The Globe also reveal a new area of friction between the inquiry and government lawyers.

The inquiry was informed a week ago that Canada's former top military police officer, retired navy captain Steve Moore, had documents that he wanted to turn over to the inquiry.

However, Mr. Moore and his lawyer had to sign a pledge preventing them from passing the documents to the inquiry.

In a letter sent to the inquiry Monday, Mr. Préfontaine said Mr. Moore's documents first have to be reviewed to remove sensitive information.

His letter comes after Mr. Préfontaine had already told the inquiry that key documents – such as logs showing that Canadian military police opened investigations into whether detainees risked torture – won't be declassified in time for the hearings.

The inquiry had asked to be on a special legal schedule that would exempt it from Section 38 and allow it to conduct closed-door hearings instead of the more stringent format sought by Ottawa.

But Defence Minister Peter MacKay turned down the request. “The existing scheme continues to be appropriate for the commission,” the minister wrote to commission chairman Peter Tinsley.

Mr. MacKay's office also will not extend Mr. Tinsley's term, which ends Dec. 11, raising the prospect that a more government-friendly commissioner will be appointed before the end of the inquiry.

“I encourage you to … start your career planning as soon as possible,” Mr. MacKay wrote last month to Mr. Tinsley.