According to a draft leaked to the media last month, the cabinet of right-wing Prime Minister Viktor Orban wants to amend the constitution by creating a new category of emergency -- "terror threat situation" -- that if declared would enable it to issue decrees, suspend certain laws, and modify others.
Among some 30 proposed changes are controls on the Internet, domestic deployment of the army, border closures, and the imposition of curfews in areas affected by a terrorist threat.
If adopted, the changes would have "profoundly negative consequences for human rights in Hungary", the campaign group warned.
The plans will be debated in parliament when lawmakers reconvene from February 15 following a winter break.
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After losing a parliamentary supermajority last year, Orban's ruling right-wing Fidesz party needs the support of at least some opposition lawmakers to pass constitutional amendments.
So far, however, talks between Fidesz and opposition parties have not led to compromise, and the draft will be proposed in its current form, a government official said last week.
Last month, several hundred demonstrators protested in the capital, Budapest, against the plans.