Sir Jeffrey Donaldson has said he will not take up his Stormont seat until the UK government addresses the protocol.
The DUP leader was elected as an assembly member for Lagan Valley on 5 May.
But he has said he will remain as a Westminster MP for the same constituency until he is satisfied that the protocol is “resolved”.
Friday is the deadline for either resigning his new assembly role or his Westminster seat.
But under assembly rules he can co-opt another DUP politician to replace him at Stormont without the need for a by-election.
Read more here.