Car rental firm Hertz has terminated its contract with Ryanair after disagreements with the airline’s recent GDS deals.
Hertz allege that Ryanair’s agreement with GDS distribution companies represents a breach of contract, a claim it disputes.
All existing bookings will be honoured and customers will still be able to modify these bookings online.
However, Ryanair said the two firms had recently extended their partnership until 2020 and that it will now "pursue Hertz for breach of contract and damages".
Ryanair CEO Michael O'Leary said: "We regret Hertz's decision to end our car hire agreement at such short notice today, at a time that will cause maximum inconvenience to our customers during the peak travel period.
"We have had a long and successful partnership with Hertz, and it’s a pity that this has ended in such an unfortunate and untimely manner...
"We apologise sincerely to our customers for the absence of any car hire services on the Ryanair website from 1200 today, however this decision has regrettably been forced upon us by Hertz’s short notice this morning."
Earlier this week, it emerged that Ryanair is set to launch flights to Amsterdam this winter.