Former Polish interior minister Mariusz Kaminski and his deputy Maciej Wasik were detained by police and taken to prison on Tuesday after being convicted of abuse of power.
The move was condemned by the nationalist Law and Justice (PiS) party, of which they are members, as "an illegal kidnapping and a violation of all democratic rules".
However, members of the new, pro-European coalition government have said that it shows nobody is above the law.
Below are some of the main events that resulted in their conviction.
Anti-corruption agency
Mr Kaminski was first elected a member of parliament in 1997 and was re-elected in 2001 and 2005. He resigned in 2006 to become the head of the Central Anti-Corruption Bureau.
Political opponents said he and his associates pursued corruption with excessive zeal, using methods they said sometimes circumvented laws and hounding innocent people.
In 2009, Mr Kaminski and Mr Wasik were accused of abuse of power for allowing agents under their command to use entrapment in an investigation. Both have denied wrongdoing.
Pardon
In 2015, Mr Kaminski and Mr Wasik were found guilty and sentenced to three years in prison. They appealed.
A few months later, after PiS came to power, president Andrzej Duda pardoned both men, allowing Mr Kaminski to become interior minister.
Lawyers questioned whether Mr Duda was entitled to pardon them before an appeals court issued a final ruling. The Supreme Court said last year that the case should be reopened.
Court's final decision
After reopening the case, Mr Kaminski and Mr Wasik were sentenced in December to two years in prison. On Monday, a court issued orders to take both men to prison.
Police entered Poland's presidential palace to detain the two on Tuesday. Prime minister Donald Tusk had earlier accused Mr Duda of obstructing justice after the two lawmakers appeared at the palace, prompting police to search for them in cars leaving the building.
Hundreds of protesters gathered in front of the palace and in front of a police station where the two were being held. The crowd chanted "Free political prisoners" and "Shame!"
In protest against his detention, Mr Kaminski started a hunger strike, while Mr Duda said he was deeply shaken by the arrests and vowed he would not rest until Mr Kaminski and Mr Wasik were freed.
