LONDON (AP) – The head of the police service in Northern Ireland has warned that any Brexit deal seen to threaten the United Kingdom could lead to disorder.

Simon Byrne told the BBC on Wednesday that there was potential for unrest among communities who consider themselves loyal to the U.K.

Byrne says the “loyalist community has at times shown it can mobilize quickly, bring large numbers of people on to the streets and engage in public disorder in support of their cause.”

The Democratic Unionist Party has vociferously objected to elements in Prime Minister Boris Johnson’s deal. They fear that proposals which treat Northern Ireland differently will bolster economic ties to the Republic of Ireland.