Dublin Bus could lose €150,000 a day, if planned strikes go ahead next month.
Drivers are taking action over plans to sell one in ten routes to private companies - Bus Eireann services will also be affected.
The Head of the National Transport Authority says European authorities aren't forcing the agency's hand to introduce public tenders for bus routes.
The NTA's decision to open up 10 per cent of routes to private firms has caused a row with unions - who are threatening seven days of strike action at Dublin Bus and Bus Éireann.
NTA CEO Anne Graham says the pay and conditions of any staff transferred will be protected - but she couldn't say the same for any existing or future staff at the private operators.
She says there is no EU requirement preventing the NTA from assigning direct contracts to Dublin Bus or Bus Eireann in the future.
