OTTAWA -- Treasury Board president Jane Philpott resigned Monday from the federal cabinet, saying she's lost confidence in the way the Trudeau government has dealt with the SNC-Lavalin affair.

"A minister must always be prepared to defend other ministers publicly, and must speak in support of the government and its policies," she said in a resignation letter to Prime Minister Justin Trudeau. "Given this convention and the current circumstances, it is untenable for me to continue to serve as a cabinet minister."

Philpott's resignation comes just less than a month after former attorney general Jody Wilson-Raybould resigned from cabinet amid allegations that the Prime Minister's Office improperly pressured her to stop a criminal prosecution of Montreal engineering giant SNC-Lavalin.

Conservative Leader Andrew Scheer tweeted that the second resignation demonstrates "Justin Trudeau's government is in chaos." He called again for Trudeau to resign and for an RCMP investigation of the affair.

Like Wilson-Raybould, Philpott said she intends to remain a Liberal MP -- for Markham-Stouffville outside Toronto, in her case.

Philpott is good friends with Wilson-Raybould, who delivered bombshell testimony last week accusing officials of relentlessly pressuring her and even issuing veiled threats to try to get her to co-operate in helping SNC-Lavalin avoid a criminal prosecution. The company is a pillar of Montreal's business community and a major player in infrastructure projects both inside and outside Canada.

"Unfortunately, the evidence of efforts by politicians and/or officials to pressure the former attorney general to intervene in the criminal case involving SNC-Lavalin, and the evidence as to the content of those efforts have raised serious concerns for me," Philpott wrote.

"The solemn principles at stake are the independence and integrity of our justice system. It is a fundamental doctrine of the rule of law that our attorney general should not be subjected to political pressure or interference regarding the exercise of her prosecutorial discretion in criminal cases. Sadly, I have lost confidence in how the government has dealt with this matter and in how it has responded to the issues raised."

Philpott has been widely seen as one of Trudeau's most capable ministers. As minister of health, she worked with Wilson-Raybould in legalizing medical assistance in dying. As minister of Indigenous services, she oversaw drastic reductions in the number of long-term advisories on water safety on First Nations reserves.

She was moved to Treasury Board in mid-January in the same shuffle that saw Wilson-Raybould moved out of the justice portfolio into veterans affairs. Treasury Board is a less-visible ministry concerned with the nuts and bolts of government operations but the president effectively holds the government's purse strings, overseeing all federal spending. Philpott took over the post from Scott Brison, who retired from politics.

In Victoria, Border Security Minister Bill Blair said he is "very saddened" by Philpott's resignation.

"Jane Philpott has done an outstanding job in all of her portfolios and served Canadians exceptionally well," he said, adding that he's pleased she intends to remain in the Liberal caucus.

Whether she will is not certain. Trudeau has been pondering whether Wilson-Raybould can stay in caucus and run as a Liberal candidate in this fall's federal election -- a matter on which he said earlier Monday he's still reflecting. He will now presumably have to add Philpott to his ruminations.

Blair refused to speculate when asked if he thinks more ministers might yet resign. But he reiterated his own support for Trudeau and the government he leads.

"I have great confidence in the team and the leadership of the prime minister."

But Liberal backbencher Celina Caesar-Chavannes, who announced last week she won't seek re-election, tweeted her support for Philpott, as she has done repeatedly for Wilson-Raybould since the SNC-Lavalin controversy erupted a month ago.

"When you add women, please do not expect the status quo. Expect us to make correct decisions, stand for what is right and exit when values are compromised. Thank you Γåòjanephilpott for articulating this beautifully," Caesar-Chavannes wrote.