Opposition MPs investigating potential improper lobbying by Rahim Jaffer are asking the government to disclose details about dealings they have had with the former Tory MP.

Jaffer and his business partner, Patrick Glemaud, testified before the Standing Committee on Government Operations last Wednesday to answer allegations of improper lobbying on Parliament Hill.

They denied the charge, saying they had not registered as lobbyists with the federal government because they have never received funds from any client for lobbying work.

But on Friday, Environment Minister Jim Prentice said Jaffer met with one of his staffers -- regional affairs director Scott Wenger -- in April 2009 and that Jaffer was acting as a representative of a green technology company.

"Why didn't the Conservative government (come forward), at that particular time, when they knew that Mr. Jaffer's company was making overtures towards a number of ministers?" Liberal MP Siobhan Coady asked Sunday on CTV's Question Period.

New Democrat MP Pat Martin also questioned the timing of Prentice's announcement.

"Where's the accountability of the ministers that allowed this to go on? It only became a problem to them when it the front page of a national newspaper," Martin told Question Period.

Allegations of improper lobbying first surfaced in a Toronto Star report earlier this month.

Tory MP Tom Lukiwski defended his colleagues, saying that it doesn't fall to politicians to report inappropriate lobbying activity.

"It is the responsibility of the individuals to register with the lobbyist commissioner -- it's not the responsibility of the government," he said.

"To suggest in some way that the government was derelict in its responsibility is absolutely false."

Jaffer and Glemaud are partners in Green Power Generation Corp., a firm that promotes sustainable technologies and renewable energy products.

Coady, Lukiwski and Martin all sit on the Standing Committee on Government Operations, which is probing allegations of improper lobbying against the two men.

Toronto businessmen Nazim Gillani, who has been linked to Jaffer, will appear before the committee next week.

Coady said she intends to ask Gillani about meetings he had with Jaffer last September, and what he took away from those meetings.

According to a Toronto Star report, the two men discussed means of obtaining government funds for business projects. Jaffer allegedly referred to a "green fund" that could be accessed.

"This is almost like an onion," Coady said. "The more you peel, the more smell there is and the more tears there are around this whole issue."