Border Agency workers at ports and airports across the country will launch a two-day strike today in protest at changes to their shift patterns.
The walkout by members of the Public and Commercial Services union will lead to disruption for travellers at all ports and airports in the UK, as well as hitting border crossing points in Calais, Dunkirk and Coquelles in France, officials warned.
PCS general secretary Mark Serwotka said: "Far from saving money, these plans will increase costs unless there are also job cuts, and we believe this is what the Border Agency is planning.
"Our members perform vital roles in keeping our borders secure and we cannot accept cuts or changes that put this at risk."
A BAA spokesman said: "Despite the improvements we've made to Heathrow, we don't control immigration and queues reflect badly on the UK's reputation - not just ours.
"We hope that UKBA urgently resolves its industrial relations problems for the sake of the travelling public. In the meantime we will do all we can to minimise disruption."