It is the third day of a cyberattack on the Metropolitan Opera that has prevented the institution from selling tickets.

The attack has hit the Met Opera’s website, box office and call center — crippling the opera company’s ability to serve its customers. The Met Opera says it normally processes more than $200,000 worth of tickets each day. Its credit card orders for the Met Opera Shop are also down, according to a spokesperson.

Rush ticketing, a program popular with bohemian types, has been a particular challenge. The system sells extra tickets on the day of the show at a cheaper rate than the standard price. The Met Opera’s sales systems have been down since early Tuesday morning.

The Met Opera said it has not yet determined the source or reason for the attacks, but added that it is working with outside cybersecurity experts. The FBI is also aware of the attack.

In its reporting, the New York Times suggested Russia could be behind the attack, due to the Met Opera’s support for Ukraine and its crackdown on artists close to President Vladimir Putin.

The FBI and the Department of Homeland Security told members of Congress late last month that China poses the biggest long-term threat to American cybersecurity. The Cybersecurity and Infrastructure Security Agency, the branch of DHS that is in charge of cybersecurity, has said both China and Russia pose a great risk to American government and cultural organizations.

The cyberattack comes as Congress weighs $885 billion in national defense funding that would focus heavily on cybersecurity programs. The House approved the funding Thursday.

Correction: A previous version of this story misstated the amount of money Congress is considering to defend against cyberattacks. The story has also been updated to reflect a House vote.