Irish telecoms company eir said it's considering its options after rival BT was fined £6.3m for failing to share information during a major contract bid.
After a complaint from eir, communications watchdog Ofcom said BT's network division had failed to give eir the same information as BT's own bid team.
BT admitted liability for its failings while the companies had been tendering for a nine-year public sector telecoms contract worth between £50m and £400m. Eir had previously held the contract since 2007.
Ofcom said that its rules require BT's network arm to treat its wholesale customers equally, as they rely on the network to provide their services.
Gaucho Rasmussen, Ofcom's director of enforcement, said: "BT's network arm broke our rules by failing to treat a rival company and BT's own bid team equally during the tender for a major public sector contract in NI. Our fine reflects how important these rules are, and how seriously we take compliance."
BT won the bid for the NI public sector shared network (NIPSSN) contract to provide shared data transfer services and calls at schools, for the police, government departments, councils and other locations.
Ofcom said BT's network arm broke rules during the tender process. It did not give eir the same information about pricing, costs and other matters that it gave to its own bid team about BT's fibre to the premises on demand product (FOD). But Ofcom said it did not believe the breaches were deliberate.
Ofcom said its fine included a 30% cut to reflect that BT had co-operated and admitted liability.
Philip O'Meara, regional director eir Business NI, welcomed the finding that BT "unduly discriminated" against eir.
"The size of the fine imposed by Ofcom on BT illustrates the gravity of BT's behaviour. We firmly believe that had BT complied with its regulatory obligations, we would have retained the NIPSSN contract," he said.
"We are considering our options in light of the decision and BT's admission of liability. Eir Business NI is keenly committed to its customers and to ensuring a fair and competitive market place for telecoms services."
Ofcom said it had not considered whether the breaches affected the outcome. A BT Group spokesperson said: "We regret the level of service we provided to this communications provider during this tender process in NI. We've co-operated with and accepted Ofcom's findings and have already put measures in place to prevent this happening again. We also continue to review how we can improve our service.
"Ofcom recognises that these errors weren't deliberate and that we took a number of steps to comply with the regulatory obligations. Based on Ofcom's decision, we don't believe this impacted the tender outcome."