Plaid Cymru's leader in the House of Commons, Liz Saville-Roberts, has signed a letter organised by the Green Party MP Caroline Lucas calling on the Speaker to table an early motion to challenge Boris Johnson "consistent failure" to be honest.
The letter to Sir Lindsay Hoyle was also signed by Ian Blackford of the Scottish National Party, Sir Edward Davey of the Liberal Democrats, Colum Eastwood of the Social Democratic and Labour Party, and Stephen Farry of Alliance.
However, Labour Party leader Sir Keir Starmer did not put his name to the letter.
The letter states that the UK Prime Minister's "lack of truthfulness" is endangering the "reputation and standing" of the House.
The parties also state their belief that Johnson's behaviour amounts to "a contempt of the House".
The letter lists several examples of the PM providing "misleading information", which they believe "undermines" the reputation of the Parliament as a whole.