The firm has now extended its previous cancellations for an additional four weeks amid the coronavirus pandemic.
They have now announced that all TUI holidays reserved before June 11 will be canceled.
Their Marella cruises are also canceled until June 30.
TUI River Cruises traveling up to and including November 25, 25 have also been discontinued.
However, the company says that those who travel after their dates, their vacations continue to work as planned and will be continually reviewed.
Customers whose vacations are canceled will automatically receive a refund credit for the full value of their vacation.
Those wishing to receive a cash refund should contact TUI directly after receiving confirmation of a refund credit.
A TUI spokesperson said, “Unfortunately, due to travel restrictions in effect, we are canceling the TUI vacation until June 11 and the Marella Cruises vacation until June 30. We would love to take you on vacation, but as it is not possible at the moment.
“We still have 140,000 reservations affected by the new cancellations and have contacted all the customers affected by the changes before May 13. In total, that’s nearly 900,000 customers.
“We are committed to helping all of our customers as quickly as possible and will issue refunds by date. “
TUI is the latest travel agency to publish an update on overseas travel. While some airlines are starting to plan routes, others have remained stuck due to ongoing restrictions.
Holiday parks across the UK have also extended their closings until the end of May, with Britain still stuck.