Passengers hoping to get away for the half-term and Platinum Jubilee weekend have faced cancellations and long delays at airports this week.
EasyJet and British Airways are cancelling flights every day and passengers at airports including Heathrow, Gatwick, Manchester, Bristol and Dublin are experiencing long delays due to staff shortages after thousands were let go during the pandemic.
The Prospect union, which represents thousands of staff across air traffic control, in airports and in aviation engineering, said things could get worse before they get better.
Garry Graham, its deputy general secretary, said: "Unions warned the government and aviation employers repeatedly that slashing staff through the crisis would lead to problems with the ramp up post-pandemic.
"The government point to the furlough scheme but ignore that it ended well before the majority of international restrictions on travel came to an end.
"Now we see staff shortages across the industry, with huge reliance on overtime to get by day-to-day.
"In many areas, like air traffic control, overtime is only a temporary sticking plaster. So, things could get worse this summer before they get better."
Ministers have placed the blame on airports and airlines, saying the Department for Transport has been telling them for months they needed to get ready for the half-term rush and hire more staff.