Both the Conservative and New Democrat parties are expected to support the proposal, which will also send the matter to the procedure and House affairs committee for further study.
The committee could recommend that the House declare Del Mastro's seat vacant, triggering a byelection.
The move comes just days after Del Mastro was found guilty on three counts of violating Canada's election laws. Although he wasn't present in the House for Tuesday's debate, he's expected to be invited to address the committee in his own defence.
In a brief ruling delivered just after question period, House of Commons Speaker Andrew Scheer confirmed that it was up to the House to decide how to proceed after last week's verdict.
He then invited New Democrat House leader Peter Julian, who was the first to rise on a question of privilege related to the case, to make the case for his motion, which would, if passed, immediately suspend Del Mastro from the chamber and send the matter to the procedure and House affairs committee for further study.
That would go one step further than the proposal initially put forward by government House leader Peter Van Loan, who has proposed to refer the question to committee before taking any direct action against Del Mastro.
But even before the ruling came down, Van Loan had made it clear that the government would likely support the committee if it recommended suspension.
Instead, he announced that the government would vote in favour of the NDP motion. The Liberals, however, have argued that Del Mastro should be expelled, not simply suspended, as they believe the law makes it clear that anyone convicted of an illegal practice under the Election Act is no longer eligible to sit in the House.
Del Mastro will lose his sessional allowance for the duration of his suspension.
NDP accuse Tories of protecting Del Mastro's pension
Earlier in the day, the New Democrats accused the government of attempting to protect their former Conservative caucus colleague Dean Del Mastro from a private member's bill that would prevent MPs convicted of serious offences from collecting a full parliamentary pension.
In its original form, the bill — which stands in the name of Conservative MP John Williamson, who formerly served as Prime Minister Stephen Harper's communications director — would have applied to any MP convicted of an offence prosecuted by way of indictment with a maximum sentence of not less than two years.
Instead, they would be given a lump sum payment that would cover all payments into the plan, as well as any interest accrued.
On Tuesday, Conservative MP Tom Lukiwksi, who also serves as parliamentary secretary to the government House leader, put forward an amendment that would limit the new rule to a specific list of criminal offences — bribery, theft, breach of trust, frauds on the government, perjury, obstruction of justice and forgery, among others.
But the pension penalty would no longer be triggered by a conviction under the Canada Elections Act, regardless of the offence.
NDP challenges PM over move
In response, New Democrat MP Craig Scott put forward a sub-amendment that would have explicitly added election-related offences to the list, but the Conservatives voted it down, and used its majority to pass Lukiwski's initial amendment.
During question period, New Democrat Leader Tom Mulcair challenged the prime minister to defend that move.
"The amendment proposed by the government, and approved by all the government members of that committee, would only help one person, the member of Parliament from Peterborough," he said.
"Does the prime minister consider that moral?"
In response, Harper argued that there was no need to expand the definition.
"The government has already passed legislation indicating that, should a member be suspended from the chamber, the case is that he ceases to participate, from that point forward, in the MP pension plan" — a bill that, he noted, the NDP had opposed.
In cases like that of Del Mastro, he continued, "we expect the member to be suspended without pay."
The budget implementation bill passed last spring freezes the pensions of MPs or senators suspended from their respective chambers.
But it does not provide for permanent withdrawal of pension benefits, nor does it appear to have any effect on parliamentarians convicted of offences after leaving office — or of those who are not hit with a suspension while still in office.
Sponsor of bill backs change
Williamson, however, told CBC News that he never intended his proposal to apply in cases like that facing Del Mastro.
"I originally proposed crimes with a maximum punishment of two years and argued it be increased to five years — indictable offences — during House debate in June 2013," he noted.
"I don’t think Dean Del Mastro comes close to either threshold, at one year maximum."
In fact, Del Mastro would not have been affected by the bill in its initial form, as he was prosecuted by way of summary, and not indictable offence.
Not only does Williamson agree with government's proposal to limit the provision to a list of specific crimes, he said actually suggested it himself, based on consultations with MPs and reflecting on the House debate.
"My proposals during committee were all five-year indictables," he recalled.
"The opposition … seemed to agree with my reasoning, at the time."
Williamson's bill will return to the House for a final vote later this fall.
Del Mastro, meanwhile, will have to wait until the same committee hands down its recommendations on his fate to learn whether he will be permitted to take his seat in the House pending a successful appeal.