Tui has extended the suspension of holidays to the Balearic Islands and Canary Islands for UK customers until August 4.
The UK’s biggest tour operator had previously cancelled trips to the Spanish islands up to and including Friday.
Its holidays to mainland Spain remain suspended until August 10.
The Foreign and Commonwealth Office reimposed a warning against non-essential travel to the country on Monday.
This was a day after Spain was removed from the Department for Transport’s exemption list for the 14-day quarantine requirement.
Tui is operating additional flights to Greece and Turkey this weekend to enable affected holidaymakers to switch their destinations.
The firm’s managing director Andrew Flintham said more than 70% of customers with cancelled trips are rebooking to travel over the same period or in the coming weeks but to a different location.
He went on: “The summer holiday period is the most important time of year for travel operators and we are therefore doing everything we can to help customers get their well-deserved holiday.
“The health and safety of our customers and colleagues is always our highest priority.
“Importantly, we also call upon the UK Government to work closely with the travel industry and remove the blunt tool approach to quarantine and consider the rapid introduction of regional travel corridors.
“The level of uncertainty and confusion created this week is damaging for business and customer confidence in travel.”