The government is set to give an update on the green list for travel later this month.
Lockdown restrictions for travel were eased on May 17, meaning that people could travel abroad for their holidays for the first time in months.
But in the Government's most recent update on June 3, Portugal was taken off the green list and moved to amber. Nowhere was added to the green list.
A statement on the Tui website said: "The government has confirmed that their list of green, amber and red countries will be reviewed every three weeks. We expect the next announcement to be around the week commencing 21 June."
This means that the next update could come on Thursday, June 24, although this has not been officially confirmed.
Most popular holiday destinations are currently on the amber list, meaning travellers must self-isolate at home for 10 days if they return after the changes are implemented.
11 places are currently on the green list, but many are not accessible due to travel rules on arrival.
