Leitrim County Council administration staff will retain their 34 hours 45 minute working week following a Labour Court Recommendation on Monday, September 10.
Local government managers had sought to standardise the working week for local authority administrative employees at 35 hours.
Council outdoor staff already work a 39-hour week.
But unions argued that increasing working hours would constitute a reduction in a pay rates and was precluded under the Croke Park Agreement.
Leitrim County Council admin staff along with Roscommon and Longford come in just 15 minutes under 35 hours a week.
Cavan workers have a 33 hours 45 minute working week. The shortest working week is in Galway county at 32 hours 55 minutes.
The LRC has recommended that the 18 local authorities which currently have a 35 hour working week will retain it. Those who currently work between 34 and 35 hours will retain their existing arrangements.
All those who work below 34 hours will see their working hours increased to 34, with part time staff seeing a pro-rata increase.
The Trade Union Impact said the binding ruling would result in a longer working week for approximately 5,000 staff.
All newly recruited or promoted staff will work a standard 35 hour week.
The Labour Court said the recommendation was on an interim basis pending the emergence of public service wide proposals on the establishment of a standard working week.
The new arrangements are expected to be implemented on 1 March 2013.
The Eurofound agency, which provides expertise advice on living and working conditions, industrial relations, and managing change in Europe said that the average working week in Ireland is 38.2 hours.
The Organisation and Working Time Act 1997 states that the maximum average working week for many employees cannot exceed 48 hours - this can be calculated over a number of months.