The National Transport Authority (NTA) is proposing to put 10% of Bus Éireann services out to tender from 2021.
The routes that they have proposed to be tendered are largely in the Dublin commuter belt.
The NTA has also recommended keeping Dublin Bus services at their 2019 level for the following five years.
However, they said they will review routes and services once the final Bus Connects network is agreed.
It comes as the authority prepares to sign a contract with Bus Éireann from December 1, 2019, to the end of November 2024 and it will exclude the routes which they propose to put out to tender.
Anne Graham, Chief Executive Officer of the NTA, said: “Dublin Bus and Bus Eireann now have a greater level of certainty so that can plan for the next five years, and of course they can also tender for services where appropriate.
“Private bus operators will be able to compete for some routes while the public will always have a decent and reliable Public Service Obligation 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.”
SIPTU representatives have condemned the proposal saying it was "ideologically driven".
SIPTU Organiser, John Murphy, said: “We are totally opposed to the proposals to remove 10% of the Bus Eireann services from the state operator in 2021 with the intention to openly tender such services at that point. This is a flawed ideologically driven agenda which will result in the further privatisation of our public bus services.”
He said that union members supported the decision to award public service contracts to Dublin Bus and Bus Eireann from next year but did not agree with the arguments put forward for the tendering of Dublin commuter routes in 2021.
Mr Murphy said: “Public transport services should not be privatised on the basis of spurious competitiveness arguments. Bus users are entitled to decent, reliable services, not those provided as part of a race to the bottom in standards and in conditions of work.
“We have all seen the problems associated with the open tendering of waste collection services across the State and the chaos they have created.”