The former Liberal MP says that she and Jody Wilson-Raybould's removal from the Liberal Party would have required a vote by all Liberal MP's under the Reform Act instead of just the Prime Minister making the decision.
Last week, Wilson-Raybould and Philpott were both expelled from the Liberal caucus.
Wilson-Raybould has said she was inappropriately pressured last fall by the Prime Minister's Office and others to intervene to stop the criminal prosecution of SNC-Lavalin.
Two months later, Philpott announced her resignation, saying she had lost "confidence" in the government's handling of the case.
Quebec Liberal MP Marc Miller said the Liberal caucus had agreed to not require caucus votes to expel MPs since the start of this Parliament, and was comfortable leaving the decision around expulsions up to Trudeau.
In recent weeks, the Liberal majority has scuttled a House of Commons Justice Committee inquiry into the SNC-Lavalin case and blocked the House ethics committee from investigating.
"We were expelled prior to the commencement of the Liberal caucus meeting", Philpott told the House as she registered her complaint with Regan, a procedure known as a point of privilege. Instead, Trudeau made the decision "unilaterally". That ruling stated that the Speaker could not weigh in on the possible expulsion of MPs from a caucus, and that the Speaker has "no role in the interpretation of statute nor in the conduct of these 2015 provisions".
Chinese woman arrested at Trump's Florida resort to remain in custody
But he said there is "no allegation that she is involved in any espionage". "She tells lies to everyone she encounters", he said. The incident has amplified concerns that the Florida resort where Trump and his advisers spend so much time is hard to secure.
"The will of caucus was very clear, but I made the decision", Trudeau said.
However, Chong himself said the recorded yes-or-no votes are "mandatory" - the language of the law is clear - and that because they did not take place, Trudeau acted illegally in expelling Philpott and Wilson-Raybould.
"The leader of the Opposition pretends that he will not back down and he tries to make a show out of it", Government House leader Bardish Chagger told the House of Commons on Monday.
Scheer is standing by his statements, and has dared Trudeau to follow through with the suit.
Trudeau says that while people disagree in politics, there are consequences for telling lies about one's partisan adversaries. "It's not something we're going to put up with".
Trudeau, asked about the legal threat, said Tuesday that with an election coming up, it's important that politicians be discouraged from twisting the truth and distorting reality.