Poland has accused Hungary of acting in a hostile manner by granting political asylum to a former Polish deputy justice minister accused of defrauding the state.
Marcin Romanowski, 48, is facing 11 charges in Poland, including defrauding or attempting to defraud $40m (£32m; €39m) from a justice fund meant to help victims of crime when he served as deputy justice minister under the previous Law and Justice-led government between 2019 and 2023.
"We consider the decision of Viktor Orban's government to grant political asylum to M.Romanowski, a suspect in criminal offences and wanted under a European Arrest Warrant, to be an act hostile to the Republic of Poland and the principles of the European Union," Polish foreign minister Radoslaw Sikorski wrote on X on Thursday night.
"Tomorrow we will announce our decisions."
On Friday, the foreign ministry said it was summoning Hungary's ambassador to the country and would request the European Commission to launch proceedings against Budapest if it fails to fulfil its EU obligations.
Mr Romanowski was responsible for the justice fund under the previous government that lost power in 2023's election.
An audit found that only 40% of the funds' resources went to crime victims and former prisoner rehabilitation, and that contracts were issued at the minister's discretion without due competitive process.
Mr Romanowski denies the charges.
He fled to Hungary, saying he would not receive a fair trial in his homeland because of politicised prosecutors and judges under Poland's current pro-EU coalition government under Prime Minister Donald Tusk.
Such reasoning was mocked by governing officials given that the Law and Justice-led government Mr Romanowski served in was widely condemned by international judicial bodies, the European Commission and European courts for introducing reform that politicised the judiciary.
Mr Tusk's government is trying to undo that reform because it created a two-tier judicial system of judges appointed under Law and Justice and older judges, some of whom do not recognise the new judges because they consider their appointments unlawful.
Until Thursday night, the 48-year-old opposition MP had not been seen for almost two weeks.
He reportedly had not used his phones or bank cards since 6 December and failed to attend a court hearing three days later that ruled he be remanded in custody before trial.
On Thursday, a European Arrest Warrant was issued by a Warsaw court acting on prosecutors' information he had fled to an EU country.
There had been speculation that Mr Romanowski was in hiding in Hungary.
On Thursday, Hungarian Prime Minister Viktor Orban said the current Polish government was treating Hungary as an enemy and he would offer refuge to anyone facing political persecution in Poland.
Mr Orban and Poland's Law and Justice party share ideological goals even though they fell out over Russia's invasion and war against Ukraine.
They broadly agree that what they consider a liberal EU-elite is driving Europe away from its Christian traditions and eroding member states' sovereignty.
Mr Romanowski is reportedly a member of conservative Catholic group Opus Dei, who issued a denial earlier this week that the MP was being hidden by them.
In October 2022, he told a Polish Catholic radio station that LGBT+ was "institutionalised deviancy".
A year later he advocated the death penalty, even for minors, after a 16-year-old boy was beaten to death by teenagers.