The European Commission, the executive body of the EU, has begun the process of enacting Article 7 of the EU Treaty against Poland, citing "a clear risk" of "a serious breach" in the rule of law due to perceived threats against an independent judiciary.
Over the past two years, "Polish authorities have adopted more than 13 laws affecting the entire structure of the justice system in Poland," the EC said in a statement on Wednesday.
The EC's concerns over the ruling, rightwing populist and nationalist Law and Justice (PiS) party's policies have grown over the past two years, since the party won an outright majority in 2015 - the first party to do so since the transition from communism to democracy.
The EC says the PiS government's judiciary reforms stack the courts with friendly judges, by giving the president much discretionary power to extend the mandate of Supreme Court judges, and imposing a younger retirement age on already-serving magistrates, among other reasons.
These moves contribute to a "lack of an independent and legitimate constitutional review and judicial independence", the EC claimed.
Witold Waszczykowski, Polish foreign minister, dismissed the EC's concerns on Wednesday, saying Poland was "importing [legal] solutions that already exist in many EU member states".
Waszczykowski said the EC was applying a different standard to Poland, which held its first free elections in 1990, after the fall of the Soviet Union.
"We do not agree to double standards if there, in other European countries, the so-called 'old democracies', these solutions can exist, while in the Polish so-called 'new democracy' these solutions are not accepted by EU officials," Waszczykowski said.
Article 7 has never been used by the EU and requires four-fifths of the EU's 28 member states - 22 - to agree that Poland's moves constitute a "serious breach" before sanctions can be imposed.
It remains to be seen if this many EU members would agree to sanctions for Poland. Hungary has stated it will not support the move.
The Eastern EU, which includes mostly former Soviet satellite states, has seen a wave of rightwing populist governments in recent years that have received criticism from Western member states.
Hungary's Fidesz was one of the first rightwing, populist political parties to seize power in the east.
Viktor Orban, the prime minister, famously said in 2014 that he wanted to create an "illiberal" democracy in Hungary, which has been sent to the European Court of Justice (ECJ) for laws that target foreign-funded NGOs and the Central European University, a higher education institution known for its international student body and support of liberal democracy.
The Czech Republic, Poland and Hungary were similarly sent to the ECJ for not accepting their share of refugees under a 2015 resettlement programme.
Hungary and Poland have taken no refugees, while the Czech Republic has taken 12.
The EC move gives the Polish government three months to respond to its concerns. For now, it is largely seen as symbolic.
Polish President Andrzej Duda signed into law the judicial overhaul that puts courts under political control on Wednesday evening, just hours after the EC announcement.