The Progressive Conservatives say they filed two freedom-of-information requests related to Christine Melnick and her involvement with invitations to the debate.
The first request went out in 2012 and the second just this year after Melnick was kicked out of caucus.
The Tories say an email that implicated the former immigration minister was in the second package of information but not the first.
Tory house leader Kelvin Goertzen wonders why the email wasn't included in the first package two years ago.
The NDP government did not immediately respond to a request for comment about the Opposition's accusation.
"Perhaps the government could just come out and tell us why they didn't release this email to begin with two years ago, why this one was withheld and covered up," Goertzen said Friday.
The party will file a complaint with the ombudsman if the government doesn't address the discrepancy, he added.
Premier Greg Selinger removed Melnick, who spent a decade in the NDP cabinet before a shuffle last fall, from caucus in February after she contradicted him about who was behind the immigration event.
Melnick initially denied ordering civil servants to invite government-funded immigrant service agency workers to watch a legislature debate — even if it meant taking the afternoon off work.
Last December, the provincial ombudsman revealed Melnick was behind the plan, and said the use of civil servants raised questions about partisanship in the bureaucracy.
Selinger said he and his staff were involved in planning the debate, but had no part in the invitations.
Melnick broke ranks and said Selinger's staff were involved from the start and had told her she would have to take the blame to protect the premier. She was turfed from caucus the following day.
The Tories are calling for an inquiry to find out who is telling the truth.
(CJOB, The Canadian Press)