The agency probing the archives of the former secret police in communist Romania may have to be abolished in its present form following a court ruling.
Dan Voiculescu waged a lengthy battle against the CNSAS
The constitutional court said parts of the law creating the National Council for the Study of the Securitate Archives (CNSAS) were unconstitutional.
Experts say the decision means that all the agency's rulings since its inception in 1999 could be struck down.
CNSAS has ruled that some key public figures had been Securitate informers.
The constitutional court found in favour of a challenge by Dan Voiculescu, the former leader of the small Conservative Party.
CNSAS had declared him in 2006 an informer, and he had lost a challenge against that ruling in the lower courts.
During a hearing against Mr Voiculescu, his lawyer called CNSAS an abusive body that selected the material it wanted and hid what it did not want.
He said the ruling against Mr Voiculescu was politically-motivated.
The head of the Supreme Council of Magistrates (CSM), Lidia Barbulescu told the Mediafax agency all the CNSAS rulings from its inception to the present day are null and void.
The vast Securitate archive has been kept under wraps
According to the constitution, parliament has to draft a new law in accordance with the constitutional court's ruling.
The body replacing the CNSAS would have reduced powers in deciding who had collaborated with the Securitate.
"The scrapping of the institution blocks the access of the citizens to their own Securitate file and the right to know their torturers," Claudiu Secasiu a member of the direction of the CNSAS said.
"We now hear a law is unconstitutional eight years after its adoption - this is unheard of."
The Securitate compiled files on many of Romania's citizens during the communist regime and had an unknown number of informers, believed to be in the hundreds of thousands.
Citizens have the right to read their own file and public figures have to declare whether or not they collaborated with the Securitate.
CNSAS has unmasked a number of public figures - former ministers, members of parliament, journalists, top clerics - as informers of the Securitate.
Its rulings have been controversial, since the bulk of the archive was handed in to the CNSAS by the Romanian Intelligence Service - the successor of the Securitate - as late as 2006, 17 years after the fall of the communist regime, raising questions over its authenticity and integrity.