Venezuela's chief prosecutor and an ally of President Nicolas Maduro has said the decision by the Supreme Court to take over legislative powers from the National Assembly violates the law.
Luisa Ortega, seen as a Socialist party loyalist, has expressed "great concern" with the situation.
The ruling effectively dissolves the elected legislature, which has been dominated by the president's opponents.
Critics say the development takes the country closer to one-man rule.
In her annual report, Ms Ortega said: "[The measure] constitutes a rupture of the constitutional order. It's my obligation to express my great concern to the country."
It comes after months of consolidation of power by Mr Maduro, who is locked in a political struggle with the centre-right opposition.
The Organisation of American States (OAS) described the move as the "final blow to democracy in the country".