A Tory Brexiteer is rallying support for a no confidence motion in Speaker John Bercow.
Former minister Crispin Blunt intends to table an early day motion, or EDM, when MPs return from their break on Tuesday.
He is making the move over Mr Bercow's perceived "bias" on Brexit.
EDM's are not allocated any time in the parliamentary timetable and are rarely debated or voted on.
However, they are used by MPs as a vehicle to express their views on a particular issue.
Strong support for a motion of no confidence would be embarrassing for Mr Bercow and add to the pressure on him to say when he intends to step down.
Mr Bercow had previously indicated he would stand down in the summer after 10 years in the post but said he now intends to carry on.
Mr Blunt's intervention follows a series of controversial rulings by the Speaker.
A number of these were widely considered to favour Remain supporters, the side the Speaker backed in the referendum himself.
Mr Blunt has written to all MPs seeking their support for his EDM.
He said he hoped to get a "minimum" of 100 MPs to sign to make it a "substantial motion" and to provide "cover" for others who wished to join them.
In a statement, Mr Blunt acknowledged they were in "totally unprecedented territory".
He said the impartiality of the Speaker was an "indispensable condition" for workings of the House.
"Even his most partisan supporters for the positive changes he has delivered as Speaker do not now seriously dispute his bias in the conduct of our affairs," he said.
"But it now goes way beyond the Brexit debate. The public should never underestimate how far reaching the implications of these powers are for our democracy."
Mr Bercow's office declined to comment on the statement from Mr Blunt.
