Drivers at Dublin Bus are split over a new cost-cutting plan at the company.
Members of the National Bus and Rail Union (NBRU) accepted the deal with 60% in favour but Siptu members have voted to reject it by a margin of just 51-49%.
The long-running row led to a three day strike in August as management aims to save about 11 million euro.
NBRU general secretary Dermot O'Leary said his union would continue to fight against any plans to privatise 10% of bus routes in the city.
"Our member's decision to accept these proposals should be viewed in the context of the constant and unfair focus on our member's terms and conditions over the last 18 months brought about by a financial crisis not of their making," he said.
"The Government's responsibility in providing a public bus service for the citizens of the state should not be abdicated at the altar of a policy driven by the desire to place profit ahead of service."
Siptu's John Murphy said drivers cannot endure any more cuts.
"Unfortunately, they (the proposals) do not form a firm enough basis for an agreement which will ensure that Dublin Bus continues to provide an efficient and cost effective public transport service," he said.
The latest set of proposals on cost-saving at the company were drawn up by former Siptu national organiser, Noel Dowling, and management consultant, Ultan Courtney.
The dispute has also seen a deal brokered in the Labour Court and accepted by all other Dublin Bus workers except the drivers.
Leo Varadkar, Transport Minister, and Alan Kelly, junior minister in the department, urged the unions to take the overall results of ballots among drivers and push ahead with the deal.
The ministers said the unions had been made aware and accepted that the deal on offer was the best that could be achieved.
"There is no other solution to the financial challenges facing the company," they said.
"Any strike will be prolonged as it is hard to see how it could be resolved given that all the industrial relations processes of the state have already been exhausted and there is no basis for any further intervention.
"There will be no winners and all sides will be worse off."
Dublin Bus said it was going to push ahead with the Labour Court Recommendation as the ballots combined meant about 55% of drivers were willing to support the cost cutting.
An implementation date will be announced shortly, the company said.