The tenth Tory MP has publicly called for Boris Johnson to resign "in the best interests of the country" as the Prime Minister continues to battle to save his premiership.
Peter Aldous, who has represented the Suffolk constituency since 2010, said he has come to the decision after a "great deal of soul-searching".
Mr Aldous has sent a letter of no confidence to the 1922 Committee.
Mr Johnson faced this call to quit as he travelled to Ukraine to hold crisis talks on how the UK will bolster the nation's defence against potential Russian "aggression".
In the Commons yesterday, Tory grandee Andrew Mitchell told the PM he no longer "enjoys my support".
Expressing his concerns, Mr Aldous said on Twitter : "After a great deal of soul-searching, I have reached the conclusion that the Prime Minister should resign.
"It is clear that he has no intention of doing so and I have therefore written to the Chairman of the 1922 Committee of Backbench Conservative MPs, advising him that. have no confidence in the Prime Minister as Leader of the Conservative Party.
"I have never taken such action before and had hoped that I would not be put in such an invidious position.
"Whilst I am conscious that others will disagree with me, I believe that this is in the best interests of the country, the Government and the Conservative Party."
When asked if the PM was worried about another Tory MP calling for his resignation, the Prime Minister's official spokesman said: “You have seen the Prime Minister seek to address the concerns of MPs in the House for a number of hours yesterday, so I can point you back to those comments.
“Obviously at the moment he is in Ukraine, focused on the challenges there.”
It comes as Downing Street made a dramatic U-turn and confirmed they will reveal if the PM has been given a fine for breaching lockdown rules.
Previously Number 10 refused to commit to telling the public if the PM was given a fixed penalty notice.
Police are investigating 12 gatherings in Downing Street and Whitehall, including several Mr Johnson is believed to have attended himself.
Cornered Mr Johnson lashed out at Labour leader Keir Starmer yesterday accusing him of not prosecuting Jimmy Savile.
