Transdev, which operates the Dublin Luas, has lost the contract to run the service after operating it for the last 22 years.
The contract is worth an estimated €1.75 billion.
An email to staff this morning - seen by RTÉ News - said that Transdev Dublin Light Rail had not been selected by Transport Infrastructure Ireland and the National Transport Authority for the next Luas Operations and Maintenance contract.
"This is clearly very disappointing news for our company. We are proud of the service we provide every day and of the role our teams have played in operating and developing Luas over more than two decades, maintaining a strong safety record and supporting the growth of the Luas light rail network across Dublin," Transdev Dublin Light Rail said in the statement.
It said that in line with public procurement requirements, the process now enters a mandatory standstill period of 14 days.
"During this time the contract cannot be formally concluded, and all bidders are entitled to review the decision. We will carefully consider the outcome and assess our position over the coming days," it added.
The company stressed that nothing changes in its day-to-day operation for now.
"Our priority remains delivering a safe, reliable and high-quality service for passengers and communities across Dublin," it stated.
"We will communicate again once the standstill period has concluded and we are in a position to outline next steps and what this means for the company and for employees," it added.
In 2024, Luas recorded 54 million passenger journeys, reflecting a strong and sustained recovery in use after the Covid pandemic.
Transport Sector Organiser for SIPTU John Murphy told RTÉ News that the transfer of the contract will take place in September.
Mr Murphy said Luas workers are protected by EU legislation that covers these types of takeovers.
He said while there will be a period of uncertainty for workers between now and September, the Transfer of Undertakings (TUPE) legislation covers workers terms and conditions.
Keolis, a large French multinational, is the preferred bidder following the tender process, Mr Murphy said, adding that there were three in the running including Transdev.
Transport operator Keolis is working in conjunction with British firm Amey, a maintenance contractor company.
Mr Murphy said this is not the first attempt by Keolis for contracts here having previously bid unsuccessfully for the LUAS contract renewal and the NTA contract.
This will be its first contract in Ireland, although it holds significant contracts globally.
There is now a two week cooling off period for unsuccessful bidders to appeal.
Mr Murphy said SIPTU is not expecting any developments in the next few weeks.
He said it may be closer to the summer before Keolis is likely to engage with the union.
