The fine comes after a back-and-forth between Spirit and at least one lawmaker, California Sen. Barbara Boxer (D), over the DOT price rules that took effect Jan. 24.
Spirit placed a pop-up ad on its website that says “new government regulations require us to HIDE taxes in your fares," and Boxer said the airline was not being honest with its customers.
"I have been shocked by the failure of your airline to tell the truth in an email sent to your customers earlier this week as well as warnings posted on Spirit.com," Boxer, a member of the Senate Commerce, Science and Transportation Committee, wrote in a letter to Spirit CEO Ben Baldanza this week.
Spirit and two other airlines, Southwest and Allegiant, have filed a lawsuit challenging the DOT price rules. Spirit and AirTran Airways, which is owned by Southwest, were fined a combined $90,000 last year for violating older DOT pricing rules in advertisements such as emails, tweets and on their websites.