EL PASO, Texas -

The Food and Drug Administration is recommending all blood banks in the U.S. test their blood for Zika, not just those in affected areas.

United Blood Services, the main blood bank in El Paso, told ABC-7 it has been testing for about a month.

The testing will require all underage donors, most of which donate during high school blood drives, have a parental permission slip. Before the change, only 16-year-old donors needed the slip.

The new requirement is hitting schools hard. El Dorado High School is hosting its blood drive Monday but only 50 students had turned in their permission slips as of Friday. With a senior class of 1,100 students, the school is doing everything it can to make sure there is a big turnout.

"We're gonna do an all-call to all the parents over the weekend to let them know that if their child did sign up to donate blood, to remind them that they will need a permission slip. We're gonna have it up on our website so parents can download it and make sure their child comes with it on Monday," said Terrie Maya, one of the school's blood drive organizers.