The son of the European Council president is being questioned by Poland's parliamentary commission as part of an investigation into one of the country's biggest financial scams.
The questioning is seen by many as part of the current ruling party's effort to undermine its political foe, former prime minister Donald Tusk, in Poland and in the EU.
Mr Tusk's son, Michal Tusk, had worked as spokesman and consultant for an airline that was a subsidiary of Amber Gold financial, a business that turned out to be a pyramid scheme.
During Wednesday's hearing, the commission wanted to know how Michal Tusk got the job.
Amber Gold operated between 2009 and 2012 when Donald Tusk was Poland's prime minister.
The commission wants to know why Mr Tusk's government failed to stop the scheme.