Senior figures from Poland's previous government are to be questioned by lawmakers over the alleged use of spyware to target critics.
An inquiry will examine claims the Law and Justice (PiS)-led administration used the powerful Pegasus software to monitor opponents' phones.
The PiS government - which lost power in October - has previously denied the accusations.
PiS leader Jarosław Kaczyński is among those who could be questioned.
Ex-prime minister Beata Szydło, former justice minister Zbigniew Ziobro and former interior minister Mariusz Kamiński are all also set to be called to testify.
New justice minister Adam Bodnar said last week he was shocked by the scale of the hacking.
The commission's head Magdalena Sroka - whose party has joined the new coalition government - said no one now doubts the spyware was used by the Polish security services.
"We were all lied to by PiS, who initially tried to deny they bought the Pegasus system...today, probably no one doubts that Pegasus was used by the Polish services," she told reporters ahead of the commission's first sitting.
Pegasus purchase
Last year the European Parliament accused Poland and several other member states of using Pegasus spyware against journalists, politicians, lawyers and businesspeople.
It came after a European Parliament delegation heard claims the Polish Central Anti-Corruption Bureau (CBA) paid 25 million zloty ($6.2 million) to buy the Israeli-manufactured Pegasus spyware five years earlier.
It was alleged the government used money from the state Justice Fund - which is intended to help crime victims - and the software was deployed to monitor the phones of at least 10 politicians, businesspeople and prosecutors who opposed the PiS administration.
The PiS-led government admitted buying the spyware but said it had been used legally to combat organised crime.
Phones hacked
Krysztof Brejza, from the new government's largest political grouping Civic Coalition (KO), will also testify. According to the European Parliament report, Mr Brezja's mobile phone was hacked when he was KO's campaign manager during the 2019 parliamentary election.
However PiS members were reportedly also hacked - RMF FM radio claimed the spyware was used against Beata Szydło's successor, PiS prime minister Mateusz Morawiecki.
Deputy commission head Marcin Bosacki said members would examine the use of money from the Justice Fund to buy the spyware, as well as identifying exactly who was put under surveillance.
PiS denials
Former interior minister Mariusz Kamiński said the commission was created to take political revenge on PiS politicians.
In a post on X he accused the commission of "manipulation, partisanship and playing political games with Poland's security" and insisted government agencies had always operated within the law.
Last month, Mr Kamiński and his deputy Maciej Wąsik began a two-year prison sentence for falsifying documents when they headed the CBA in 2007. They claimed they were "political prisoners".
The pair were released after 13 days when President Andrzej Duda, a PiS-ally, pardoned them.