Mariusz Kamiński and Maciej Wąsik were detained on Tuesday night, escalating a standoff over the case between President Andrzej Duda and Prime Minister Donald Tusk, the Reters news agency reported.
Kamiński and Wąsik, MPs with the conservatives Law and Justice (PiS), were due to be taken to prison after being convicted of abuse of power while heading Poland's anti-corruption service CBA.
Earlier in the day, they appeared with the head of state at an official event in the presidential palace.
The prime minister said that the president, a Law and Justice ally, could be held accountable for obstructing justice, according to news outlets.
"We would like to inform you that in accordance with the court order, the persons concerned by the instructions were detained," the police said on the X social media platform on Tuesday night.
Interior Minister Marcin Kierwiński said that "everyone is equal before the law."
Law and Justice politicians called police's actions "an illegal kidnapping and a violation of all democratic rules."
Hundreds of Law and Justice politicians and supporters gathered outside the presidential palace, chanting "free political prisoners," the Reuters news agency reported.
Later on Tuesday night, the protest continued outside a police station where the two MPs were being held, private broadcaster Radio Zet reported.
Tusk, a former president of the European Council, became prime minister following election in October, which saw pro-European parties win power after an eight-year rule of Law and Justice.
Law and Justice's reign was marked by a dispute with Brussels over democratic standards, such as judicial independence, according to news outlets.
In 2015, after Law and Justice came to power, the president issued a pardon for Kamiński, allowing him to become interior minister, the Reuters news agency noted.
Some lawyers called Duda's decision into question as it was issued before a final ruling by an appeals court, according to news outlets.
In June 2023, Poland's Supreme Court said the case should be reopened, the PAP news agency reported.
In December 2023, Kamiński and his deputy at CBA, Maciej Wąsik, were sentenced to two years in prison for abuse of power, the Reuters news agency reported.
Szymon Hołownia, the speaker of Poland's Sejm (lower house of parliament), said the verdict meant that Kamiński and Wąsik had lost their MP's mandates.
Meanwhile, they have denied that and said they would attend the Sejm's next sitting.
The president on Monday met with the Sejm speaker, seeking to convince him that his 2015 pardon for Kamiński was valid and the court had no right to give a second verdict, but the two did not reach an agreement, the Reuters news agency reported.
Hołownia on Tuesday postponed this week's Sejm sitting until next week to "ensure the dignity of the Sejm and social calm," according to news outlets.
The prime minister said he "fully supports" the top lawmaker's decision.
This week, MPs were due to vote on the 2024 budget, according to the Sejm office.
They have until the end of January to send it to the president for him to sign; otherwise the head of state can dissolve parliament, the Reuters news agency reported.
Source: IAR, PAP, wp.pl, Reuters, Radio Zet