OTTAWA -- The Liberals are ramping up the heat on Intergovernmental Affairs Minister Peter Penashue, calling on the elections watchdog to take a closer look at past campaign spending by their political rival.

In a letter distributed to media Sunday, Interim Liberal Leader Bob Rae asked the commissioner of Election Canada to launch a formal investigation into allegations of campaign misspending during the last election by the Tory minister.

This summer, Penashue's former campaign manager, Reginald Bower, issued an apology for oversights in Elections Canada paperwork after it was learned the campaign team spent nearly $4,000 more than the legal election limit.

Opposition parties have also raised questions about media reports suggesting there appears to have been a sweetheart deal the minister's team arranged with a Labrador-based airline during the 2011 campaign.

Documents in the reports suggest the carrier "wrote off all but $7,000 worth of the $18,163 in travel by individuals with the Penashue campaign other than the candidate," Rae writes.

Penashue has also been accused of attempting to circumvent rules around campaign loans.

Rae said if true, the allegations could be considered infringements of elections laws and could call into the questions the results of a tight race.

The minister won his Labrador riding by just 79 votes.

Through a spokesman, Penashue said only that "there is a new official agent in place to work with Elections Canada to correct any mistakes that were made by the previous official agent" on his campaign.

Elections Canada was not available for comment Sunday.