Leader Dominic Cardy filed a complaint Thursday, but the commissioner's office said it couldn't proceed until it received an affidavit, which was delivered Friday.
The affidavit alleges Tory backbencher Greg Davis didn't disclose financial assistance from a political party.
Davis could not be reached for comment.
The affidavit alleges that Davis's public disclosure form makes no mention of the loan.
Cardy asks commissioner Alfred Landry to start an investigation under the Members Conflict of Interest Act.
Landry's office confirmed by email it had received Cardy's affidavit, but there was no response when asked what steps, if any, would be taken.
The Progressive Conservative party has said it covered $5,125 in rent for 2011-12 for Davis's riding office. Government spokesman Bob Fowlie has also said Davis fell behind in his rent again, though Fowlie has not said how much Davis was in arrears.
Last week, Davis said he would not seek re-election in the riding of Campbellton-Restigouche Centre in September due to unspecified health reasons.
Premier David Alward said Thursday he's confident answers will come from a legislative committee reviewing Davis's constituency expenses. The committee is scheduled to meet Tuesday and its findings will be made public.