HOUSTON, Dec. 26 (Xinhua) -- United Airlines has apologized to a woman who accused the company of reassigning her first-class seat to a Texas congresswoman without her consent.

Jean-Marie Simon, a teacher from Washington D.C., wrote in a Facebook post last week that the airline gave her first-class seat, which she paid for and selected in early December, to U.S. Representative Sheila Jackson Lee as she was about to board a home-bound flight on Dec. 18 at George Bush Intercontinental Airport in Houston.

Simon wrote that a United attendant told her that her ticket was not in the system and that united.com had changed her reservation about an hour before boarding.

The attendant said another passenger had been upgraded to her seat, and they couldn't disrupt what was already done, wrote Simon.

United spokeswoman Andrea Hiller told the Daily News on Monday that the company's internal system showed Simon canceled her flight within United's mobile app and released her seat to next person on the airline's upgrade list, which happened to be Jackson Lee.

However, Simon denied she ever canceled her flight.

The spokeswoman said the airline has reached out to Simon to offer its apology and a 500-U.S. dollar travel voucher as compensation. Meanwhile, Jackson Lee defended herself in a statement that she "asked for nothing exceptional or out of the ordinary and received nothing exceptional or out of the ordinary."

In April, United Airlines sparked outrage after a passenger was dragged off an overbooked plane to make room for its own staff.