The country's human rights watchdog has called upon the Constitutional Court to rule the anti-communist National Security Act as unconstitutional on the grounds that it violates the freedoms of expression and thought.

The National Human Rights Commission on Wednesday submitted an opinion to the court ahead of an open hearing on the Act on Thursday, the first time the legality of the security law will be reviewed by the Constitutional Court.

Arguing that clauses within the Act unconstitutionally infringe upon freedoms of expression, thought and conscience, the watchdog said that a lack of clarity in the text opens the door to the arbitrary interpretation and application of law.

Adopted in late 1948, the Act criminalizes praising or propagating activities of "anti-state" organizations or their members, as well as producing, importing, copying, possessing, transporting or selling "enemy-benefiting" materials.

The Commission pointed out that compared to 1948, there is a noticeable gap between the two Koreas in terms of their economic and military capacities, saying such acts by South Koreans now would pose little risk to society.