The Liberals want Elections Canada to investigate donations to Intergovernmental Affairs Minister Peter Penashue's 2011 election campaign. (Sean Kilpatrick/Canadian Press)

Interim Liberal Leader Bob Rae is raising more questions about donations made to the campaign of Intergovernmental Affairs Minister Peter Penashue during the last federal election.

Rae asked the commissioner of Elections Canada on Tuesday to investigate five donations that came from staff at the corporate headquarters of Pennecon Limited.

The donations were first reported by CBC News.

The donations were received on May 4, 2011, two days after the federal election. They came from the same St. John's postal code.

Three donations are for the limit of $1,100, while two others are for half that amount, $550.

Rae says the donations are unusual because they come from a large postal station in the west end of the city, not a residential area.

The Liberal leader says he wants Canadians to be assured that the donations came from the personal funds of the donors and not from the company or from any other sources, both of which are prohibited under the Canada Elections Act.

"In light of the nature of these donations, namely, the simultaneous timing of the donations, their dollar value, the postal address given and the shared place of employment of the donors — I feel it would be prudent to conduct a deeper examination by you and your office," Rae wrote in his letter.

Rae asked the commissioner earlier this week to conduct a formal probe into what he calls spending irregularities by Penashue's campaign in the riding of Labrador during the 2011 election.

Penashue has blamed rookie mistakes and says he's working with Elections Canada after spending thousands of dollars more than the legal limit in the campaign.

His former campaign manager has apologized to Elections Canada for mistakes and missing paperwork.