Welwyn Garden City's Beefeater is set to become a Premier Inn restaurant that only hotel guests can dine at.
The Stanborough Road site is a popular dining spot for the town's residents, but Whitbread - which owns both the restaurant and hotel chain - has informed customers changes will be coming later this week.
"We are writing to let you know that we've announced plans to make changes at some of our restaurants," read an email to diners.
"Unfortunately, The Stanborough Beefeater in Welwyn Garden City will be changing to a Premier Inn restaurant and will only service those staying in the hotel after July 5.
"We apologise for any inconvenience this will cause.
"The really good news is that we have another Beefeater near to you - Moor Mill, Beefeater located in Radlett, or Ware, Beefeater located in Ware."
The decision comes after Whitbread announced plans to "unlock" 3,500 new hotel rooms at existing Premier Inn sites by converting "lower-returning branded restaurants" back in April.
Speaking about the proposals earlier this year, chief executive officer Dominic Paul said: "I recognise that these changes will be unsettling for affected team members and we are committed to working hard to enable as many as possible of those affected to stay with Whitbread."
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