BUCHAREST (Reuters) - Under scrutiny during its first six-month EU presidency, Romania would damage the rule of law if it carries out plans to decriminalize some forms of corruption and grant an amnesty to offenders, the head of the European Commission said on Friday.

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The leader of the ruling Social Democrats, Liviu Dragnea, has a conviction for vote-rigging and is therefore barred from becoming prime minister. He denies any wrongdoing.

Dragnea has been pushing for changes including a decree that would grant prison pardons and amnesty, which would also help his case. He is widely seen as the real power holder in Romania, though he holds no government job.

“If an amnesty were adopted, as some in this country envisage, it would be a step back in the rule of law,” the head of the executive Commission, Jean-Claude Juncker, told a joint news conference with Romanian President Klaus Iohannis.

Even though the European Union is built on compromises, there can be no negotiations about legal principles, he said.

An attempt by the Social Democrats to decriminalize several corruption offences at the start of 2017 triggered Romania’s biggest street protests since the 1989 fall of communism.

In November, lawmakers approved a bill pushed by the Social Democrats and their coalition partner that would cancel wiretap evidence used to prosecute past corruption cases and could wipe out hundreds of convictions, including Dragnea’s.

The centrist opposition challenged the bill in the Constitutional Court, which could issue a ruling as early as Jan. 16.

“INTERNAL DIFFICULTIES”

Speaking later at a news conference with Romanian Prime Minister Viorica Dancila, Juncker urged the authorities to set aside internal disagreements during the country’s EU presidency, which began on Jan. 1.

Juncker added: “I heard the prime minister tell me that she has a clear wish not to cast any shadow on the Romanian presidency by exporting internal difficulties to Europe.”

Last month Juncker caused an uproar in Romania by expressing concern in a German newspaper that Bucharest might not be ready to take the helm of the EU. Asked if he stood by these comments, Juncker said he would not take them back.

President Iohannis, a centrist, has also been critical of the government’s readiness to lead the EU and strongly opposes its amnesty proposals, but tried on Friday to project an image of unity.

“We are very well prepared for the difficult period ahead of us now,” he said.

During its EU presidency, Romania faces Brexit in March, European Parliament elections in May and tough talks on the next long-term EU budget. The second-poorest EU country, Romania joined the EU in 2007.