British Prime Minister Theresa May criticized the Trump administration's "zero tolerance" immigration policy and the separation of migrant children from their parents as "wrong" during Prime Minister's Questions on Wednesday, adding that "the pictures of children being held in what appear to be cages are deeply disturbing."

Why it matters: The United Kingdom is one of the United States' closest allies, and President Trump is set to make his first visit to the country as president next month. His plans to visit have already been fraught with controversy amid the threat of protests — and the immigration issue is sure to add fuel to the fire.