Staff moral at NI's 26 councils is at "rock bottom" amid uncertainty over amalgamation plans, public service union Nipsa has said
A reduction in council numbers to 11 was due next year under the Review of Public Administration (RPA).
NIO minister Hugo Swire had warned a decision had to be taken by the end of May to allow elections to be planned.
However, a meeting of the Executive on Thursday put back a decision on the move for two weeks.
After the meeting, Environment Minister Edwin Poots said: "We're coming back to this in two weeks time to make a decision, so there will be considerable pressure upon the Executive to finalise that.
"In the interests of fairness, we need to reach a decision in any event, given that council staff have been in Limbo for some time."
So far, £9m has been spent preparing for the changes.
Earlier, Mr Poots told the BBC that councils sharing their resources would save more money than the amalgamation process.
The minister said it was "confused" to suggest that amalgamation "automatically equates to efficiencies", emphasising that the £100m cost was a problem in itself at a time of cutbacks.
"However, it may be possible to do that, and that is one of the options that is on the table," he added.
Mr Poots said that "amalgmation, in and of itself" would not save as much money as collaboration, the sharing of facilities between different council areas.
The minister's own proposals on how collaboration should be advanced were rejected by the Northern Ireland Local Government Association, which is coming up with its own plans.
However, Mr Poots told the BBC on Thursday these were not far enough advanced to allow a "solid decision" to proceed.
Bumper Graham of public service union Nipsa said the uncertainty over councils meant staff morale was "at rock bottom".
"We have had a series of stop-go announcements, political posturing and millions wasted on consultants," he said.
"Nipsa is demanding that an announcement is made today and that immediate intensive negotiations are held with the union to protect the interests of staff and to ensure that essential public services are not further damaged."
The Review of Public Administration, which also includes reforms to the health and education sectors, was meant to save the Executive more than £400m over the next 25 years.
The Executive's agreement in March 2008 to cut the number of councils was seen as proof that the DUP and Sinn Fein could cut a deal on a big issue.
NIO junior minister Hugo Swire wrote to Mr Poots on Monday urging him to decide by the end of the month if council elections scheduled for May 2011 would be on the basis of 11 or 26 councils.
He said the failure to bring before the Assembly an Order to give effect to the new local government boundaries was "a matter of some concern and urgent action is now required".
Mr Poots said there would be "options put on the table, from doing nothing to going through to an 11-council model for next year".
He added: "What I am insistent on is that whatever option we go down, it is an option that will actually pass savings on to the public."