The German government expressed to the ambassador "its continued serious concerns over domestic political developments in Romania," said the spokesman, Steffen Seibert, in a statement.
The rebuke from Berlin came as Romanian Prime Minister Victor Ponta travelled to Brussels in a bid to convince European Union leaders that his drive to oust the president did not threaten democracy.
Moves to impeach President Traian Basescu and curb the powers of the Constitutional Court have raised concerns about domestic politics in the former communist bloc nation that joined the EU in 2007.
"In the view of the federal government, the measures taken in the past few days by the Ponta government to curtail the powers of the Constitutional Court and shift responsibility for publishing court decisions seriously endanger the principle of the separation of powers," Seibert said.
Berlin expects Bucharest to "comprehensively publish and implement all verdicts of the Constitutional Court," added the spokesman.
Basescu, who has been suspended from his functions by the parliament for now, has alleged the real goal of his opponents in the Social Liberal Union (USL) coalition is to bring the judiciary under its control.
But Basescu has himself faced counter accusations of trying to dominate the judiciary since he took over in 2004 as well as over-reaching his powers.
Senior EU officials have warned that the centre-left government's actions could slow Romania's full EU integration, including its bid to join the visa-free Schengen travel area.
The country's candidacy has been blocked by the Netherlands so far.