Airlines have warned the Home Secretary that Britain "risks gridlock" at airports over the Easter break due to staff shortages.
British Airways and Virgin Airlines are among 11 firms that have written to Theresa May in anticipation of "unacceptable" delays to hundreds of thousands of passengers travelling over the long weekend.
The UK Border Agency is under fire for a lack of staff able to carry out full security checks, which the airlines say must result in a recruitment drive or the relaxing of some of the more stringent measures currently in place.
A spokeswoman for Virgin Airlines said: "While the decision on what level of check should be made at the border is, of course, a matter for Government, we are concerned that there is currently a mismatch between policy and resource.
"After years of reducing frontline staff, returning to a 100% check system will undoubtedly mean lengthy queues at UK airports over critical holiday periods such as Easter and the Diamond Jubilee.
"If the Government wishes to continue with this policy, it must put the resource in place to make it possible or we risk gridlock at our busiest airports at a time when we hope to be welcoming millions to the UK."
More than 370,000 passengers will leave Heathrow airport between Good Friday and Easter Monday, and 200,000 will pass through Gatwick.
A spokesman for Heathrow owner BAA told the Daily Telegraph: "Immigration waiting times during peak periods at Heathrow are currently unacceptable and we have called on the UK Border Force to address the problem as a matter of urgency.
"There isn't a trade-off between strong border security and a good passenger experience. UK Border Force should be delivering both."
Meanwhile, Britons attempting to travel by rail and road face delays because of engineering works taking place on motorways and train lines.
Stretches of the M1 and M25 will be affected, and the seven million passengers travelling by train over the weekend will see disruption to travel to and from Euston, King's Cross, Liverpool Street, and Waterloo stations in London.
The Association of Train Operating Companies (Atoc) and Network Rail said there were 34% fewer replacement buses for cancelled trains this Easter compared with the same period last year.
A Border Force spokeswoman said: "We will not compromise border security, but we always aim to keep disruption to a minimum by using our staff flexibly to meet demand.
"Carrying out full checks at airports help us stop threats from terrorists, criminals and others who want to harm the UK and make sure that only those with the right to enter the UK can do so."