The country is in the process of installing a new prime minister following months of protests amid shortages of basic necessities such as fuel and food.
A state of emergency, declared last week, remains in place while the Foreign Office continues to advise against all but essential travel.
The advisory, which was reinstated in early July, doesn’t apply to airside transit through Sri Lanka’s Bandaranaike International airport near capital Colombo.
Tui had previously cancelled its Sri Lanka programme until the end of July, but this has since been extended to all holidays departing up to and on 15 August.
"We will be proactively contacting all impacted customers in departure date order to discuss their options," said Tui.
"Customers currently in resort can continue to enjoy their holiday as planned. We will continue to monitor the situation and update customers should there be any further updates. We would like to thank our customers for their understanding at this time."