The Scottish Executive is being asked to force the health service to release information about childhood leukaemia rates in Dumfries and Galloway.
Robin Harper urged the health secretary to intervene
The Greens called on Health Secretary Nicola Sturgeon to intervene after it emerged that the NHS had appealed against a landmark court ruling.
Last year the Court of Session backed the information commissioner's decision that the figures should be released.
However, the NHS is now planning to take the case to the House of Lords.
A spokeswoman for the Common Services Agency, which provides a statistical service to the NHS, confirmed that its lawyers had advised there were grounds for appeal.
"In view of the fundamental principle at the heart of this matter - patient confidentiality - we have decided to proceed with this appeal," she said.
However, Green Party leader Robin Harper said: "I would urge Scottish Executive ministers to intervene on their civil servants to abide by the court ruling and release this information.
"The law provides for safeguards and I regard the decision by officials within the CSA to pursue this matter to the bitter legal end in the face of common sense, the public interest and two decisions against them, as unacceptable."
He urged Ms Sturgeon to instruct the CSA to comply with the original ruling "without further delay or further unnecessary cost to the public purse".
An executive spokeswoman said ministers were "very sympathetic" to the case made by the Greens.
"They are currently examining the matter to establish the best way forward," she said.
The test case followed a Green Party worker's request for information about childhood leukaemia cases in Dumfries and Galloway by census ward.
The CSA said there had been 15 cases in the region between 1990 and 2001 but said it was concerned that providing greater detail could lead to the identification of living patients.
Scottish Information Commissioner Kevin Dunion ruled that the statistics should be released, but the CSA appealed against that ruling.
In December last year, the court upheld the commissioner's view that it was possible for the information to be provided in a form which would not risk identification.
However, a further appeal to the House of Lords is now planned in a bid to overturn the decision.