Bahrain's military courts are now authorised to try civilians after the government approved a constitutional change allowing the controversial move.
The island's 40-member consultative council - the upper house of the Bahraini parliament appointed by King Hamad bin Isa Al Khalifa - voted for the measure on Sunday despite wide criticism by rights' activists.
Their approval came less than two weeks after the 40-seat Council of Representatives, the parliament's elected lower house, passed it with little opposition.
Lawmakers voted 31-1 to pass the constitutional amendment, with three members on hand not voting.
Activists warn the amendment will allow an undeclared state of martial law on the island near Saudi Arabia that is home to the US Navy's 5th Fleet.
"The Bahraini king is effectively creating a police state with this de facto martial law," Sayed Alwadaei, the director of advocacy at the Bahrain Institute for Rights and Democracy, said in a statement.
Loyalists of Bahrain's rulers call the change necessary to fight extremism as the persistent low-level unrest that followed the 2011 demonstrations has escalated recently in tandem with the crackdown.
Its government forces - with help from Saudi Arabia and the UAE - crushed the 2011 uprising by its Shia-majority population and others who sought political reform.
Independent news gathering on the island has grown more difficult since the government began a crackdown on dissent in April.
Since 2011, activists have been expelled or imprisoned, and the main Shia opposition group has been dismantled.