The court, however, said on Thursday it had rejected other complaints by Slovakia's liberal president and opposition, meaning that a plan to scrap the special prosecutors' office (USP) which has dealt with serious crime including high-level graft will go ahead.

The combination of the changes, pushed through by Prime Minister Robert Fico's coalition in a fast-track legislative procedure, has alarmed the opposition as well as the European Commission and the European Prosecutor's Office.

Criticism has focused on the lack of wide debate, a marked lowering of punishments for financial crimes, and a shortening of statutes of limitations which would forever halt many ongoing investigations, even if the law took effect for just one day.

President Zuzana Caputova described the Constitutional Court's decision as "good news for democracy and rule of law".

"The system of checks and balances worked, that is the most important message to all Slovak citizens...is also a needed message to our foreign partners, that the money of European taxpayers remains adequately protected," she said.

The court did not scrap plans to abolish the Office of Special Prosecutor, which has dealt with high-level crime including cases involving senior public officials and politicians from Fico's SMER-SD party.

Fico said he was generally satisfied that the special prosecutors office would cease to exist, after he repeatedly accused it of being politically biased against him and his party.

"For me the most important thing was achieved - shutting down the prosecutor's office," he told a televised news conference. "I was myself a victim of bullying by the USP."

Caputova had argued that doing away with the USP would delay about 1,000 pending court cases which would have be shunted to other prosecution branches.

Thursday's top court decision means the affected parts of the reform will not take effect on March 15, pending further deliberations by the court that may take months.

The court acted speedily, aiming to make its decision effective before the reform law went into force.

(Reporting by Jan Lopatka in Prague, editing by Jason Hovet, Emelia Sithole-Matarise and Mark Heinrich)

By Jan Lopatka