Bupa has been granted an injunction preventing moves to make it pay millions in compensation to its rival VHI following the Tánaiste's decision to implement the so-called 'risk equalisation' scheme today.
Bupa had already been granted leave to seek a judicial review of the risk equalisation scheme and the hearing is to go ahead in February.
The health insurer, which is VHI's main competitor, said the move would involve the group having to pay out an annual subsidy of more than twice its annual profits.
"We have always said that risk equalisation makes competition and the BUPA Ireland business unviable. This remains the case," Bupa said in a statement.
"In order to protect the interests of our customers, the nearly 300 people who work in BUPA Ireland, and our business, we have successfully applied to the High Court for an injunction preventing any steps being taken to implement the Minister's decision pending the hearing of our case, which is due to be heard by the High Court on the 7th February.
"Our case is that the legislation and regulations contravene EU law and the constitution."
Mr Justice Michael Hanna restrained the Minister and the Health Insurance Authority from taking any steps whatsoever pursuant to any decision the Minister might make with regard to triggering risk equalisation.
The Tánaiste said her Department would study the matter and would seek the Attorney General's advice.