About 1,400 security officers at Heathrow Airport will strike for eight days next month.
Unite said the staff will walk out from 4 to 6 May, 9 to 10 May and 25 to 27 May in a dispute over pay - causing "inevitable disruption and delays" to passengers arriving for the King's coronation.
The union's general secretary, Sharon Graham, said: "Yet again, we have a chief executive who thinks it is acceptable to boost his earnings while he denies his own workers a decent pay rise.
"This dispute is bound to escalate with more workers being balloted and disruption set to continue throughout the summer."
Security guards at Heathrow also took part in a 10-day walkout over Easter.
That strike involved security officers at Terminal 5 - which is used exclusively by British Airways - and campus security guards who are responsible for checking all cargo that enters the airport.
BA cancelled about 5% of its flights during that walkout, and stopped selling tickets for strike days.
A Heathrow spokesperson said: "We kept Heathrow running smoothly during the first 10 days of Unite's failed industrial action, and passengers can have confidence that we will do so again this time.
"We will not let Unite disrupt the flow of visitors to the UK during such an important period for the country."
Heathrow says it has been offering a 10% pay increase as well as a lump sum payment of £1,150 since January - but claims that the union has failed to put this revised offer to their members.
Unite's regional officer Wayne King disputed this, and claimed the airport has shown a "stubborn refusal to make an offer that meets our members' expectations".
He added: "Our members have been crystal clear they are seeking a substantial permanent increase in pay.
"A small one-off lump sum payment will not alleviate the financial pressures our members are facing on a daily basis."
In other developments, Passport Office staff are preparing to strike for four days at the start of next month.
Public and Commercial Services (PCS) union members in all passport offices across the UK will walk out from 2 to 6 May in a row over pay, pensions, redundancy terms and jobs.
Action so far has been limited to some staff in some offices, but the union announced an escalation on Wednesday to include all members in all offices.
Nearly 2,000 passport examiners are already taking part in a rolling strike, but the new announcement means a further 1,000 staff - including interview officers and those in administrative and anti-fraud roles - will also take part.
Meanwhile, senior civil servants will vote on industrial action over pay for the first time in more than four decades.
The FDA union said its executive committee has voted to launch a ballot in response to the government's decision last week to give civil servants a pay rise of between 4.5% and 5%.
The union claimed the government had left it with no choice after the way civil servants had been treated.
FDA general secretary Dave Penman said: "In my 23 years at the FDA and 10 years as general secretary, I have never found myself so utterly at a loss as to why the government would want to treat our members and the rest of the civil service in this way.
"If this is, as I suspect, a tactical decision to use the civil service to send a message elsewhere then not only is it a flawed one, but once again demonstrates that there are those in government who simply do not value the civil service in the way they do the rest of the public sector."