Image caption Finance Minister Sammy Wilson said the executive had no option but to agree the increase

The executive has agreed that public sector workers should pay an extra 3.2% in pension contributions.

It did so after the Treasury threatened to cut the Northern Ireland block grant by tens of millions of pounds.

The BBC has learned that ministers attending last month's executive meeting agreed, with only the SDLP's Alex Attwood objecting.

The chief secretary to the Treasury had written warning the block grant would be cut by £4.8m a month from April.

The pension increases, proposed by London, are among grievances raised by public sector workers across the UK.

While union leaders negotiate the issue with the government in London, public sectors unions, representing teachers, nurses, civil servants and bus drivers, are among workers being balloted for strike action on November 30.

Threatening

Treasury Secretary Danny Alexander, however issued his letter threatening that cuts would rise to £140 million a year in three years time.

The SDLP's Alex Attwood told fellow ministers that they should object in line with the Scottish Executive, which dismissed the letter as threatening and not democratic. The Scottish Executive has since accepted the plan.

Finance Minister Sammy Wilson told the BBC the Stormont executive had no option.

Peter Bunting of the Irish Congress of Trade Unions said the Treasury letter showed that talks with the government in London over the issue were a farce.

Patricia McKeown from Unison said the decision was unfair.

"Why are they promoting the idea of a cut in corporation tax which will benefit the big corporates and knock almost £400m off the block grant?" she said.

"Is it that we look after a small number of elite businesses but we totally ignore the biggest workforce in Northern Ireland?

"I think big questions are going to be asked."

If strike action goes ahead, it could be UK-wide and the biggest industrial strike in Northern Ireland's history.