The National Bus and Rail Union (NBRU) has threatened industrial action following the announcement that 10% of Bus Éireann routes are earmarked for privatisation.
The announcement by the National Transport Authority (NTA) was made at the start of a consultation period on the renewal of contracts with Bus Éireann and Dublin Bus for the period 2019 to 2024.
The NTA said it proposes reducing Bus Éireann's routes by 10% from 2021, mainly involving routes in the Dublin commuter belt, and putting these out to tender, which the bus company can also bid for.
But SIPTU has condemned the move and the NBRU has threatened industrial action with its general secretary Dermot O'Leary saying it will be "vigorously opposed".
"The determination of the NTA ... to aggressively attack Semi-state jobs cannot be allowed to go unchallenged by those from across the political spectrum that profess to oppose the privatisation of State services," he said.
SIPTU organiser John Murphy condemned the proposal, saying it "was ideologically driven and would result in further privatisation of public bus services".
For Dublin Bus, the NTA says it may be necessary to privatise new routes under the Bus Connects plan.
However, it says there will not be any further privatisation of existing Dublin Bus services for the next five years.
Anne Graham, CEO of the NTA, said: "Private bus operators will be able to compete for some routes while the public will always have a good quality and reliable public service obligation (PSO) service, provided by a combination of incumbent operators and operators that are new to the market.
"We believe that competition improves services which can only be good for the customer."
Dublin Bus services to remain 'at least' at 2019 levels
The NTA envisages Dublin Bus services remaining "at least" at 2019 levels.
But it says the Bus Connects plan will not be completed in time for the new contract and there will have to be further negotiations with Dublin Bus to revise existing routes when the plan is ready.
"The scale of the changes to bus services anticipated in the Bus Connects network review, particularly the introduction of entirely new bus routes in some areas, means that the authority will need to consider further whether those particular routes will be added to the direct award contract with Dublin Bus or be competitively tendered," it said.
However, it added there will not be any reduction of overall service levels by Dublin Bus and the company can tender for any new routes.
A private company, Go Ahead, is in the process of taking over 10% of Dublin Bus services mainly consisting of orbital routes, as well as one new route. This process will be completed in January.
Noting today's announcement by the NTA, a spokesperson for Bus Éireann said that the company would "participate positively in the consultation process", and it would "determinedly focus on retaining any routes currently operated, and which may be subject to further tender".
"We recognise that both competitiveness and service quality are critical to future growth and success. In this respect, we welcome that it has been acknowledged by the NTA that our business transformation - which commenced over 12 months ago - has now helped us to achieve competitiveness on price."
"Our customer satisfaction rating is of paramount importance and continues to improve following the implementation of the most significant change programme ever in the company, after three weeks of industrial action last year.
"We are presently improving reliability and punctuality - which has also been acknowledged by the NTA - and now remain focused on delivering even higher customer satisfaction scores.
"Next month we look forward to starting operation of the Waterford City services contract, which Bus Éireann won in a competition of five bidders - and will strive to build on this success in this forthcoming PSO Contract 2019."