With egg prices surging in the U.S., some Americans are trying to lower their grocery bills by buying them south of the border. The only problem: It’s illegal to bring them back into the country, and now seizures of eggs at some U.S.-Mexico border crossings have surged more than 300%.

Since Nov. 1, egg seizures are up 91% at the agency’s El Paso field office, 301% in Laredo, 333% in Tucson and 368% in San Diego compared to the same period a year earlier, according to Customs data through Jan. 17. In most cases, the seizures involve no more than a few 30-egg flats that travelers say they purchased for themselves to take advantage of lower prices in Mexican stores, said Roger Maier, a spokesman for U.S. Customs and Border Protection.

“It’s really been a dramatic increase over the past few months,” he said.

Residents of border towns often buy groceries in Mexican stores, but some agricultural products are barred from import to the U.S., including raw eggs, which can spread Newcastle Disease and avian flu, Maier said.

“We believe a lot of people were just unaware” of the restrictions on bringing in eggs, Maier said.

In most cases, the eggs were seized from travelers who declared their purchase to inspectors at the border and consequently weren’t fined. Recently, agents have encountered “a very small number” of undeclared eggs and travelers were subject to fines, he added.

Eggs prices in the U.S. have shown some of the most jolting increases among food staples in the past year. The cost of eggs in December was 60% higher than a year earlier, according to the most recent data from the Labor Department’s consumer price index. Avian flu outbreaks and the resulting destruction of hen flocks have largely driven the price increases, though the wholesale price of eggs has eased a bit over the past month, signaling some relief ahead for consumers.