Teletext Holidays has warned 20 of its advertisers will be struck off its books on April 1 if they do not secure an ATOL.
The company has alerted its 400 TV and web advertising clients they need an ATOL, or need to be advertising products of ATOL holders, to continue using its services.
Managing director Matt Cheevers said the move would ensure all consumers booking through Teletext companies are financially protected.
Originally, as many as 75 companies did not have ATOL protection, but this had reduced to 20 by this week. Most are agents putting together dynamic packages without ATOL cover.
Cheevers said: “If you do not have an ATOL and you are selling your own product we will not feature you on Teletext.”
Civil Aviation Authority deputy director David Moesli said: “It is sensible to ensure [people buying] holidays sold on Teletext are protected.”