The boss of airline industry body IATA has blasted National Air Traffic Services (NATS) for the recent chaos at Britain's airports - and demanded the company foots the bill for the disruption.
Willie Walsh, the head of the International Air Transport Association, which represents more than 300 of the world's carriers, also questioned whether the firm should continue to hold responsibility for handling the UK's flight traffic.
It comes after hundreds of flights were cancelled - and thousands of passengers left stranded - after a computer glitch on Bank Holiday Monday caused chaos at airports in the UK and abroad, with disruption expected to continue throughout the week.
NATS chief executive Martin Rolfe said "unreliable" flight data caused the disruption, although a full investigation into what went wrong is under way.
In a statement released on Tuesday, Mr Rolfe said: "I would like to apologise again for our technical failure yesterday.
"While we resolved the problem quickly, I am very conscious that the knock-on effects at such a busy time of year are still being felt by many people travelling in and out of the UK."
But Mr Walsh, the former chief executive of British Airways owner IAG, said carriers were facing a potential bill of up to £100m due to the failure.
In an interview with Sky News, he called on NATS to clearly explain what caused the problem and said questions needed to be asked about the resilience of air traffic control computer systems.
He said: "They [NATS] should be held to account and they should pay for the expenses that have occurred... airlines are a victim in this situation, they're not the cause of the problem."
Mr Walsh added: "At the moment, I have to say, my confidence in NATS has been badly shaken and until we can evaluate the cause, and the actions taken by NATS to address this, we're going to have doubts about whether they are the right party to continue to operate this system."
He is the latest air industry figure to speak out after Ryanair boss Michael O'Leary blasted the chaos as "not acceptable". Mr O'Leary said his airline was forced to cancel 250 flights on Monday and dozens more on Tuesday.
The Civil Aviation Authority has pledged to carry out an investigation, while NATS - a public private partnership part-owned by carriers - has insisted its staff had been working hard to ensure the fault never happened again.
But Mr Walsh told Sky News: "I'm surprised that Martin [Rolfe], the CEO at NATS, is so confident that the problem won't reoccur.
"We do need to see a lot more detail before we can be satisfied that we should have confidence in NATS going forward".
He added: "It's a shocking performance from NATS, it has led to massive disruption and clearly it's unacceptable that we get this level of disruption at a peak time of the year - or indeed at any time of the year - and I think NATS have a lot of questions that need to be answered."