A group of her fans are suing Ticketmaster for a list of violations.
They allege fraud, price-fixing and antitrust violations, and accuse Ticketmaster and its parent company Live Nation of letting resellers buy most of the concert tickets.
The lawsuit is asking for a civil fine of $2,500 per violation.
That would add up to a lot of money, since about two million tickets were sold.
A Senate anti-trust panel said it would hold a hearing on the lack of competition in the ticket sales industry.
Swift has since apologized to her fans for the situation.