The Prime Minister's Office has hired a prominent employment law firm to handle an investigation into allegations against one of its senior staffers.

The PMO has asked Rubin Thomlinson LLP to be the independent, third-party investigator dealing with the complaint process involving Claude-Eric Gagne, deputy director of operations for Prime Minister Justin Trudeau.

Janice Rubin, who was hired by the CBC to lead the third-party investigation into allegations against former radio show host, Jian Ghomeshi, is a partner at the firm, but the PMO would not say whether she is involved.

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Gagne, who has been on leave since Nov. 1 pending the outcome of the investigation, says he challenges the veracity of the allegations, but is co-operating fully with the investigator, who has given him the opportunity to explain his side.

Calling in a third party to examine allegations of workplace harassment is one of the steps that can be taken under the policy governing whose who work for the federal government, although that Treasury Board policy does not technically apply to those who work in the PMO.

Last month, the Liberals proposed changes to workplace harassment rules that would include expanding the scope to include the PMO.