"This is very serious. This not some technical or legal issue, this is a political issue on a long list of provocations against the EU," Beaune said on air of BFMTV broadcaster, also pointing to risks of Poland's withdrawal from the bloc.
"Yes, this is an attack against the EU ... I want to stress that I would not like Poland to leave the EU," Beaune added.
The EU could abandon its plan of financial support for restoring the Polish economy, the senior diplomat added.
Poland's constitutional court ruled earlier that national law had primacy over EU law in areas where they contradicted each other, putting the country on a collision course with the European Commission, the EU’s executive arm.
EU Justice Commissioner Didier Reynders promised on Thursday that the bloc will make every effort to defend its core principles, after the top Polish court challenged the primacy of European Union law.
In turn, Prime Minister Mateusz Morawiecki said on Friday that Poland did not plan to leave the European Union.