NDP Leader Tom Mulcair raised the issue after reports suggested that Tory staffer Michael Sona allegedly confessed to his involvement in the voter suppression scheme at a time when he would have been on a Caribbean vacation.
Sona denies any involvement with the fraudulent robocalls.
Liberal Leader Justin Trudeau also asked about reports alleging that Jenni Byrne, formerly the Conservative Party's national campaign manager, advised a key witness in the investigation to delay an interview with Elections Canada.
Byrne now works as the prime minister's deputy chief of staff.
Prime Minister Stephen Harper denied that allegation and said his party is co-operating fully with investigators probing the alleged voter fraud in Guelph, Ont. during the 2011 federal election.