Travelodge is one of a number of firms whose customer data has been subject to an attack by hackers, it has revealed.
Details that could have been stolen include customer names, email addresses, mobile phone numbers, date of birth and/or gender.
Payment details and passwords have not been affected.
The hotel firm said that it was notified on Friday (29 June) by Typeform, a third-party company that manages its customer surveys and competitions that it had been the victim of a "data security incident".
Typeform said that unauthorised access to its server data occurred, involving files related to Travelodge.
In a statement, Travelodge said: "We were notified by Typeform of the incident on Friday 29 June 2018.
"We have worked during the weekend to isolate how the wider incident impacted Travelodge data, which customers were affected and how to contact those customers.
"As soon as that information was available, we wanted to contact customers directly."
The data affected was gathered as part of eight different online competitions dating back to last year, including a competition to win a free stay in August last year, and a Black Friday Promotion.