LONDON (Reuters) -Staff at an aviation fuel services firm at London’s Heathrow airport have voted to carry out a strike over pay, the Unite union said on Tuesday, in Britain’s latest industrial action that threatens more disruption to transport services. About 93% of union members at Aviation Fuel Services who voted were in favour of a strike after having gone without a pay hike for three years, Unite said, adding that an initial 72-hour strike would begin July 21. The union said a strike is likely to cause “considerable disruption and delays” throughout Heathrow where AFS provides fuelling se…