TUI Group has cancelled all holidays before June 11th.
At the same time, all Marella Cruises will be suspended until June 30th.
TUI River Cruise, due to launch last month, will now commence on the November 26th.
It is the latest extension from TUI Group in the midst of the coronavirus pandemic.
Most recently, the company had hoped to restart trips on May 14th, with Marella looking to begin operations at the end of May.
A TUI spokesperson said: “We are proactively contacting all customers whose bookings are impacted to offer a range of flexible options.
“Customers will receive a 20 per cent booking incentive when accepting a refund credit to move to another date, or can request a cash refund.”
For customers travelling after June 12th, TUI has extended its flexible amends programme until July 11th, so customers with bookings can amend to another date for free.
“We would like to thank customers for their patience and understanding, especially given the scale of people we are trying to help,” added TUI.