Under Washington's revised data breach law, businesses are required to notify consumers within 45 days if their personal information was accessed by an unauthorized person.
The firm was further criticised for having paid a $100,000 ransom to the hackers in order for them to stay quiet.
Washington state Attorney General Bob Ferguson is suing Uber for failing to disclose a massive data breach that left the personal information of 57 million people exposed.
The data breach resulted in almost 11,000 Washington Uber drivers having their data compromised.
The data is understood to have included names, email addresses and mobile phone numbers, but according to Uber, trip location history, credit card and bank account numbers, and dates of birth were not downloaded. "Consumers expect and deserve protection from disclosure of their personal information". They also warned that those in the United Kingdom affected should have been notified.
Europe's data protection authorities can streamline their investigations into companies, something that is exceptional, but that has happened in big cases including the Yahoo data breach earlier this year.
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Ferguson's lawsuit is the first from a state, although attorneys general in New York, Missouri, Massachusetts, Connecticut and IL have begun investigations, and the city of Chicago and Cook County have filed a lawsuit.
For its part, Uber disclosed that two individuals outside the company inappropriately accessed user data stored on a third-party cloud-based service that it uses. Uber waited more than a year, Ferguson said.
The firm has said it has a total of five million active users and 50,000 drivers in the UK.
However, Attorney General Ferguson contends that each day that Uber failed to report the breach to each of the drivers-as well as to his office-counts as a separate violation.
"We are committed to changing the way we do business, putting integrity at the core of every decision we make and working hard to regain the trust of consumers", said Nathan Hambley, an Uber spokesman.