According to the official website of the British Monarchy, those covering their formal engagements must adhere to a dress code out of respect for the royals.
"Smart attire for men includes the wearing of a jacket and tie, and for women a trouser or skirt suit," the website reads. "Those wearing jeans or trainers will not be admitted and casually dressed members of the media will be turned away. This also applies to technicians."
The Duke and Duchess of Cambridge, both 32, will visit the U.S. next month on behalf of the Royal Foundation, "other charities with which Their Royal Highnesses are closely associated" and the U.K. government. Prince William will spend time in Washington, D.C. and New York City, while Kate will stay for the duration in the Big Apple, according to Kensington Palace.