Democratic Unionist Party Jeffrey Donaldson has hit back at accusations it is not opposed to the Northern Ireland protocol.
Mr Donaldson said its “political critics” were claiming the DUP was not against the controversial protocol.
In a letter to party members, seen by the PA news agency, Mr Donaldson said that its political unionist opponents need to “wise up”.
The letter comes after senior DUP MP Sammy Wilson was loudly booed and jeered as he addressed a loyalist rally against the Northern Ireland protocol.
Mr Wilson was repeatedly interrupted as he attempted to deliver a speech at the event at Markethill in Co Armagh on Friday.
During his address, Mr Wilson compared the EU's handling of Northern Ireland in the Brexit process with Vladimir Putin's annexation of Crimea in Ukraine.
However, his comments were often drowned out as angry crowd members accused his party of botching the Brexit process.
Thousands of people attended the rally, with dozens of bands from across Northern Ireland taking part.
At one point in Mr Wilson's speech, Traditional Unionist Voice leader Jim Allister intervened and appealed to those in attendance to hear him out.
On Saturday, Mr Donaldson said in a letter: “Some of our political critics are attempting to claim the DUP is not opposed to the Northern Ireland protocol.
“At a time when I am trying to encourage greater unity in opposition to the protocol, they are seeking to undermine such unity for purely party political reasons.
“They need to wise up and recognise that our strength is in our unity.
“We have taken decisive action in our opposition to the protocol.
“It is the actions of this party in withdrawing ministers from the North-South Ministerial Council, in challenging and attempting to frustrate the checks at ports and ultimately in the resignation of the First Minister, that has highlighted that the protocol is not compatible with stable local arrangements.
"It is this party that has made clear that if the long shadow of the Northern Ireland protocol is not removed from Stormont then we will not have the stable basis, supported by both unionists and nationalists, to form an Executive."
Mr Wilson went on to accuse Mr Allister of “whipping up an anti-DUP sentiment”.
He said that some in loyalism are intent on “manufacturing disunity where none exists”, and that it undermined the message of the rally.
“Whilst Jim Allister appealed for respect, it came after he spent ten minutes on the platform whipping up an anti-DUP sentiment in a blatant act of electioneering,” Mr Wilson said.
“Whilst Sir Jeffrey has sought to work with every hue of unionism, whether he always agrees with them or not, to get a united front and common cause against the protocol, it seems Jim is only interested in using the protocol to promote his and his party’s narrow electoral interests.
“Unionism is ill-served at this time by such division.”
The protocol, introduced in the wake of Brexit, has created new economic barriers on trade between Northern Ireland and the rest of the UK.
Agreed by the UK and EU to ensure no hardening of the Irish Border post-Brexit, it has instead moved regulatory and customs checks to the Irish Sea, with Northern Ireland remaining in the EU single market for goods. The region also applies the EU customs code at its ports.
Unionists and loyalists claim the arrangements have undermined the sovereignty of the UK, but a majority of Assembly members at Stormont support the protocol, claiming it offers Northern Ireland a degree of protection from negative economic consequences of Brexit.
The EU and UK continue to negotiate in a bid to agree a way to reduce the bureaucracy associated with the protocol.
"When I addressed party members on Thursday February 3rd on the announcement of the resignation of the First Minister I said that if the protocol is left in place, then the divergence between Northern Ireland and the rest of the United Kingdom will grow and without a single vote cast, the protocol will have re-oriented our supply chains and our economy away from Great Britain," Mr Donaldson added.
“Laws will be made and implemented that impact every citizen without any local representative having shaped them or voted upon them.
“There comes a moment when we have to take tough decisions if we are to build for the future.
“While others talk about what they will do, the DUP took action.” – PA
