A government "amnesty" to the rules on airport slots is in place until Friday, allowing airlines to change schedules without facing a potential penalty.
Ministers told carriers to review their plans after chaos in May, blamed on a shortage of airline and airport staff.
British Airways said the move would help provide "certainty" to customers.
The UK's biggest airline, whose services from Heathrow Airport are likely to bear the brunt of this week's cancellations, said the measures would make it "easier to consolidate some of our quieter daily flights to multi-frequency destinations well in advance, and to protect more of our holiday flights".
Airport slots provide airlines with the authorisation to take off or land at a specified time on a specified day. In usual circumstances, the carriers risk losing the slots - and taking a hit to their business - if they cancel flights.
The Department for Transport (DfT) amnesty will give airlines a short window to hand back the slots in the summer season they are not confident they will be able to operate.
A DfT spokesperson said: "This will help passengers find alternative arrangements ahead of time, rather than face the kind of last-minute cancellations seen over the Easter and half-term holidays."
That earlier disruption prompted the government and the aviation regulator, the Civil Aviation Authority, to write to airlines telling them to ensure their summer timetables were "deliverable... based on the resources you and your contractors expect to have available".
Heathrow said the slot amnesty would "enable airlines to make early choices to consolidate their schedules, boosting the resilience of summer operations and giving passengers the confidence they deserve ahead of their journeys".
It added: "We encourage airlines to take this opportunity to reconsider their summer schedules without penalty and inform passengers as early as possible of any changes."
Tim Alderslade, chief executive of trade body Airlines UK, said it followed other measures taken by the sector.
"We will continue to work with ministers and the whole aviation ecosystem to ensure the summer peak runs as smoothly as possible for our passengers," he said.
Rory Boland, editor of Which? Travel, said the move would also allow rival airlines to step in and fly the cancelled routes.
He said: "Carriers must surrender their slots to other airlines if they are unable to fulfil them. This will help reduce cancellations and end the unsustainable practice of airlines flying near-empty planes to retain slots."
Thousands of aviation jobs were lost during the Covid pandemic and many businesses have struggled to recruit enough new staff in time to deal with resurgent demand for travel following the easing of rules.
Gatwick said it would be reducing the number of flights during summer because of staff shortages even before the airport slots amnesty was first set out by the government on 21 June,
Heathrow to date had not announced similar plans although last week it ordered 30 flights to be cancelled, saying it was expecting more passenger numbers than it could cope with.
It comes as Manchester Airport warned it would not be able to return to its pre-pandemic standards until the autumn.
Aviation industry consultant Paul Charles predicted thousands of flight cancellations would be announced this week, meaning less last-minute disruption over the summer.
But he told BBC News passengers were facing a "summer of stress".
Staffing levels remained 20-30% lower than they should be, he said, with a rise in Covid cases seeing airline and ground workers calling in sick in recent weeks.
Meanwhile, passengers face the prospect of disruption from strikes involving airline staff over summer.
Hundreds of British Airways workers at Heathrow Airport - mostly check-in staff - have voted to go on strike in July over pay, and unions are currently consulting engineers and call centre staff at Gatwick, Glasgow, Manchester and Newcastle on taking action.
Unions have also called for EasyJet cabin crew based in Spain to strike for nine days this month as part of a dispute over pay.