A diplomatic spat has erupted between Spanish and US officials after staff at Miami airport insisted on screening Spain's Crown Prince and his fiancee.
The couple were due to fly on to Spain when they were searched
Crown Prince Felipe and Letizia Ortiz, and four bodyguards, were due to catch a connecting flight at Miami when they had to undergo security checks.
Airport staff said the search had to be carried out after the couple failed to give the normal 72 hours notice.
Miami-Dade's mayor has apologised for the "apparent disregard for protocol".
The 36-year-old future king and his TV anchorwoman fiancee had flown into Miami from the Bahamas on Thursday evening, reported The Miami Herald.
Before boarding their Iberia Airlines flight to Madrid, the couple and their entourage had to pass through a security check.
They were taken to an American Airlines lounge, where they were searched by three "top-notch screeners with VIP experience", said Lauren Stover, Transportation and Security Administration spokeswoman.
She said the incident was sparked because the royal party had given only six hours notice instead of the standard 72 hours.
"The prince and his bodyguard felt they should not be subjected to the screening, but if they do not have an escort from the State Department or the Secret Service, it is required," she added. "It is the law."
Miami-Dade County Mayor Alex Penelas sent the royal family a letter of apology on the same day, calling the situation "lamentable".
"The facts I have received thus far indicate an apparent disregard for protocol and disrespect of His Highness and his delegation... I have called upon our County Manager to conduct a simple investigation into this matter," he wrote.
A Spanish consular official in Miami said it would be Consul General Javier Vallaure's decision whether a complaint should be filed.
"We don't consider this the proper way to treat our future king," he was quoted by the Associated Press as saying. "It's a breach of protocol".