The DUP would be “justified” in deploying a petition of concern to block a motion of no confidence in the Assembly speaker Robin Newton, a senior party member has claimed.
Sinn Fein will lodge the motion in the Assembly on Monday.
The party’s national chairperson Declan Kearney has called for DUP MLA Mr Newton to resign with immediate effect.
Mr Newton was criticised by MLAs last month for his decision to allow First Minister Arlene Foster to make a statement on the Renewable Heat Incentive scandal without the support of the deputy first minister.
The move sparked dramatic scenes in the Assembly, with MLAs from all parties – bar the DUP – walking out of the chamber ahead of Mrs Foster’s speech.
Mr Kearney said Mr Newton’s position had become “untenable” as a result of those proceedings.
He added: “The DUP speaker’s performance in the Assembly on December 19 totally compromised the neutrality of that office.
“The speaker is now acting as a law onto himself. That is absolutely unacceptable.
“As speaker he should be above reproach and independently accountable to the political institutions. However, he is acting without regard to the integrity of the office.
“He is now part of the problem and an integral part of the unfolding crisis and he should resign immediately.”
The speaker has also faced calls to step down from the UUP and SDLP.
However, DUP MP Sammy Wilson hinted that the DUP could potentially make use of the contentious petition of concern to block Sinn Fein’s motion.
The vetoing mechanism is intended to protect minority interests and requires the signature of 30 MLAs to be valid. The DUP has 38 seats, including the speaker.
Mr Wilson accused the other parties in the Assembly of “acting like children” adding: “One day they are targeting Arlene Foster, the next it is the speaker of the Assembly. It just illustrates the immaturity of Stormont. This whole situation has now gotten to the point of silliness and these other parties need to grow up.”