"This decree was necessary because, 18 years after the fall of the communist regime, we could not stop midway in our efforts to reveal the crimes of communism," Prime Minister Calin Tariceanu said.
The constitutional court declared last Thursday that several clauses in the law allowing access to the Securitate files were unconstitutional.
It said the National Council for the Study of the Securitate Archives (CNSAS) "was violating human rights" and acting as a "parallel judicial authority" by disclosing the involvement of several prominent figures with the communist-era secret police.
Since its foundation in 1999, the CNSAS has accused several important figures of collaboration, leading some, such as former culture minister Mona Musca, to be dismissed or forced to resign.
Under the new decree, the CNSAS may continue its work but its field of activity will be limited, Tariceanu said.
It will no longer be allowed to publish conclusions on whether politicians, lawmakers or candidates for public office collaborated with the Securitate, but individuals may continue to consult their own secret police files.
The constitutional court's decision last week caused an uproar in Romania, with several non-governmental organisations and political parties warning it amounted to a "restoration of communist forces".
A new law, taking into account the constitutional court's recommendations, is to be submitted to parliament within 45 days of the court's ruling.