Sir Lindsay Hoyle is facing mounting pressure to quit as Commons Speaker over his handling of a vote on Gaza.
SNP Westminster leader Stephen Flynn said his decision to pick a Labour motion had seen Parliament “descend into farce”.
He added his party no longer had confidence in him, and called for a Commons vote on his future.
Sir Lindsay apologised for his decision, but said he had done it to ensure MPs’ safety.
He is holding meetings with senior MPs to discuss next steps.
Thirty-six Conservative MPs have also effectively called for him to go by joining SNP MPs in signing a motion of no confidence.
There is no formal way for MPs to oust the Speaker, but the withdrawal of support from the SNP, the third largest party at Westminster, makes his position significantly more precarious.
It comes after Sir Lindsay departed from convention to allow MPs a vote on a Labour amendment calling for a ceasefire in the Israel-Hamas war during a debate allocated to the SNP on Wednesday.
The move meant Labour MPs could call for a ceasefire without backing a differently-worded ceasefire motion from the SNP, limiting a potential Labour rebellion but provoking fury among the SNP’s MPs.
