BRUSSELS, July 2 (Xinhua) -- The European Commission Monday took a new round of legal action against Poland over its judicial reform, in the latest move to bring Warsaw to heel.

The Commission launched the so-called "infringement procedure" by sending a "Letter of Notice" to Poland regarding the Polish law on the Supreme Court, which lowers the retirement age of Supreme Court judges from 70 to 65.

According to the amended law, the mandate of current judges can be prolonged by Polish president for three years and renewed once. However, the Commission argued that "there are no criteria established for the President's decision and there is no possibility for a judicial review of this decision."

Poland was given one month to reply to the letter. The commission will step up legal pressure if Warsaw's explanation fails to satisfy Brussels.

A dialogue on rule of law between them has been underway since last December when the Commission triggered Article 7 of the EU treaty against Poland over the judicial reform dispute.

Dubbed so-called "nuclear option", Article 7 has never been triggered against any EU member state before. The procedure could eventually lead to Poland losing its voting rights in the 28-member bloc.

The Commission suspected that Poland's laws reforming the Supreme Court and the National Judicial Council might be undermining the EU's rule-of-law principles.

Nevertheless, the Commission said Monday that the ongoing rule of law dialogue with Poland remains the Commission's preferred channel for "resolving the systemic threat to the rule of law in Poland."