The dispute is over a little piece of land at the end of Spain called Gibraltar. There's a rock there you might have heard of.
Gibraltar is mostly self-governing, but it's still technically a British territory. And that's been an annoyance for Spain, which has its own territorial claim on the region.
And the EU gave a nod to that claim this week. The draft guidelines for Brexit negotiations says Spain should have final say on all U.K.-EU agreements involving Gibraltar after Brexit happens.
Gibraltar isn't happy about that. The region's chief minister said the proposal was "a clear manifestation of the predictably predatory attitude" Spain holds toward the territory.
But then, Gibraltar isn't happy with the whole Brexit process, either — 96 percent of the territory's roughly 30,000 residents voted to remain a part of the EU during the Brexit referendum.