Ryanair will go offline for three days this month to comply with an Office of Fair Trading instruction to display all prices inclusive of tax and charges.
But it will do so having failed to meet a deadline for compliance by the end of January.
The delay will infuriate the trade, which has largely complied with demands to display inclusive pricing since May 2007.
A deal between the OFT and ABTA has seen the latter police members, issuing fines of up to £5,000 to a handful of companies that failed to comply on pricing.
An OFT spokesman said: “We are very disappointed Ryanair has not met the agreed date of January 31 for changing its website.” The airline argued technical difficulties prevented compliance.
On May 11 last year the OFT announced: “The deadline to include all fixed non-optional costs in the basic advertised prices of holidays has expired.” On August 9 it stated: “Ryanair will be making these [agreed] changes shortly.”
A Ryanair spokesman confirmed: “Our booking site will shut down from February 16 to 11.59pm on February 18.”
Flight details will remain available, but no one will be able to book or make changes to bookings for three days. Ryanair said passengers would be informed in advance. No extra staff will be available offline to deal with problems.
An ABTA spokeswoman said: “We are very disappointed and awaiting the next deadline. But this is about raising the industry’s reputation. If Ryanair does comply, it will have been a success.”