The Northern Ireland Protocol – which has created a trade border in the Irish Sea to protect the EU single market – would lead to laws in the province being made “in a Dublin-influenced EU”, Unionists feared.
“There are forces using the exigencies of Brexit to advance a programme of constitutional change through stealth and propaganda,” Mr Robinson said, in a newspaper article.
“My advice to those who are driving this agenda forward is as short as it is restrained. Take care.”
Some opposition would be “vented more robustly” than protest voting and “be met with greater tolerance than it deserves”, the leader of the Democratic Unionist Party (DUP) until 2015 said.
“We are perilously close to a line which, when crossed, will lock us all into a pattern all too familiar to my generation,” he added.
The article comes amid stalemate over attempts to solve the crisis affecting imports from the UK because of vast red tape created by Boris Johnson’s EU withdrawal deal.
The EU has started legal action after the UK unilaterally delayed further checks – and the two sides have not held direct talks involving ministers for one month.
Supply problems that emptied supermarket shelves have eased, but the UK government admitted they would return if ‘grace periods’ were ended, as agreed under the 2019 Protocol.
Last month, food inspections at Northern Ireland ports were suspended following an “upsurge in sinister and menacing behaviour” and graffiti appeared to describe port staff as “targets”.
The DUP has demanded the Protocol be scrapped altogether, but the UK government has rejected that – while experts warn there is no alternative to the rules it imposes.
Mr Robinson wrote: “It is too easy to either be dismissed as a scaremonger or attacked for sabre-rattling.”
Unionists believed “their rights are being violated”, he said, adding: “They reflect on the commitments they were given, and which have been appallingly broken leaving the odour of betrayal in the air.
“Those with wisdom who have their finger on the pulse should recognise the signals when a people become disenchanted with the system.”
Mr Robinson said: “It would be wrong to assume that in time Unionists will calm down and eventually acquiesce. That is not my assessment.”
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