The Supreme Court has granted an application by VHI to be allowed take part in a legal challenge by its rival Bupa to the controversial risk equalisation scheme.
The scheme is intended to compensate the State's largest health insurer, VHI, for its older membership base.
The independent Health Insurance Authority is due to make its final recommendation on the scheme to the Minister for Health Mary Harney today. The HIA is expected to urge her to introduce the scheme.
The VHI - with 1.55 million members - has said the risk equalisation scheme is vital to the future of the community rating scheme under which health insurers must charge customers the same premium for a particular plan regardless of their age or health history.
It is estimated the VHI could receive up to €33 million under the proposed scheme.
However, Bupa is seeking to have the High Court declare that the risk equalisation scheme is invalid under the constitution and EU law. The hearing of that case will open on December 7th.
Last July, the High Court ruled that the proceedings should go ahead between Bupa and the Minister for Health without the involvement of the VHI.
VHI appealed against that decision to the Supreme Court which, in a unanimous decision by three judges today, allowed the appeal. The decision means the VHI will be involved in the December action.
In a statement, VHI Healthcare said it welcomes the Supreme Court decision.
"The action taken by Bupa against the Department of Health and Children would, if successful, effectively destroy the system of community rating, which has been the cornerstone of private health insurance in Ireland for almost 50 years," VHI said.
"While VHI Healthcare has every confidence that the State will successfully defend this case, this is an issue of fundamental importance to our 1.56 million members and thus we believe we must represent their views at the legal proceedings."