Starting in May, driver’s licenses issued in Maine and South Carolina may not be accepted as identification at airports and federal buildings unless the states work out a last-minute agreement with the federal Department of Homeland Security.

The states are refusing to ask the agency to extend the deadline for applying new layers of security in their identification systems as required under the federal Real ID Act. Congress passed the legislation in 2005 with the intention of making it harder for terrorists to obtain driver’s licenses.

The final Real ID regulations were released Jan. 11, and states have until Monday to request an extension of the compliance date. Without an extension, driver’s licenses from Maine and South Carolina will no longer be deemed valid as identification at airports and federal buildings starting May 11, the original date of compliance. As an alternative, travelers could use passports.

“If an individual shows up at an airport on May 11 or later and their licenses are from any state not in compliance, it’s effectively showing up without federal identification of any kind,” said Amy Kudwa, a spokeswoman for the Department of Homeland Security. “Individuals in those scenarios will have to have added security and screening.”