Justice Minister David Ford has formally apologised over an administrative gaffe which former part-time police reservists fear may have compromised their personal security.
As a review got under way into the blunder which identified the ex-support officers, Mr Ford also initiated an urgent security assessment of the threat level against the former RUC personnel.
But he side-stepped demands for his resignation over the "regrettable incident", which may yet lead to an emergency debate when the Assembly returns from summer recess next month.
Senior sources said the envelopes containing three items of correspondence in relation to the £20m gratuity fund payout for the part-time reservists were too large, which allowed the contents to slip down.
The main letter informing individuals of how much they will be entitled to - after deductions for tax and national insurance - was then visible, with the strapline RUC Part-Time Reserve Gratuity.
Now a helpline - 028 9052 2444 - has been set up for officers who may have to move from their homes to protect themselves and their families.
"This breach of security is mind-boggling," said Ulster Unionist MLA Ross Hussey.
"The persons responsible might as well have just sent a list of the names and addresses of the people affected to local dissidents."
Lodging a formal complaint with the department over its "incompetence and insensitivity", Mr Hussey, who chairs the part-time officers' group, added: "Some of our members were forced to resign because of terrorist threats, some had to move away.
"Now, because of the inability of the department to deal with a simple task of putting letters into envelopes, my colleagues feel their security has been breached."
The DUP's Policing Board member Ian McCrea said: "Former members of the RUC and their families have been through more than enough after 30 years of violence. It is not acceptable that such basic security measures were not put in place when letters were being dispatched."
Traditional Unionist leader Jim Allister said Mr Ford should not only "hang his head in shame" but consider if he should resign.
"Jeopardising the security of former security personnel is a serious matter (and) Mr Ford is very precious about the status of his position as a minister," he said.
But Mr Ford responded: "I share the concerns raised and want to apologise for any distress this has caused. I have initiated a security assessment and have established a helpline for individuals who have concerns."
At its peak there were 4,500 members of the RUC Reserve, an auxiliary force which, along with the UDR, replaced the B Specials after publication of the Hunt Report in 1969.
Under the terms of the Police Act (NI) of 1970, the RUC Reserve, initially consisting of 1,500 men, came into existence. During the Troubles 102 members of the Reserve were murdered.