“I flew to Los Angeles under the rules set for board members of Lufthansa,” Verdi leader Frank Bsirske told the paper. “But I underestimated how explosive it would be in the eyes of the public.”
Bsirske, who was heavily criticized last week over the incident, also said he would pay for the flight.
His vacation - five weeks in the South Pacific - was interrupted with calls for his resignation on Saturday after Bild reported he had flown free in first-class on Lufthansa shortly before Verdi members walked off the job at the airline. The strike continues to hamper Lufthansa's service.
The trade union and Lufthansa announced a tentative wage agreement on Friday after going on strike on Monday.
The paper reported that Bsirske and his wife flew business-class from Berlin to Frankfurt am Main on July 8 and then flew first-class via Los Angeles to the South Pacific.
Bsirske was entitled to the free flights because he is on the supervisory board of Lufthansa AG, but his timing raised eyebrows across the political spectrum in Germany and has led to calls for his resignation.
“Mr. Bsirske should stay in the South Pacific. If he does not resign now, union members should kick him out,” Dirk Niebel, secretary-general of the Free Democratic Party, told Bild on Saturday.