A federal appeals court in Pasadena heard from attorneys Tuesday who say President Trump's proposed border wall violates more than 30 environmental laws.
Ahead of the hearing, about 20 people gathered for a rally outside of the courthouse in opposition to the wall.
The Center for Biological Diversity, the group bringing the legal challenge, said the Trump administration skirted dozens of environmental laws using waivers that have expired.
The Department of Homeland Security argues that national security concerns outweigh environmental laws.
The court has been asked to issue an expedited decision. A ruling could still take weeks or months.