President Barack Obama came under a barrage of criticism Wednesday as he declared almost a half-million acres of rugged desert terrain along the U.S.-Mexico border a national monument.

It was the largest swath of land to be set aside for that purpose since Obama took office. But while praised by environmentalists, the move generated criticism from lawmakers in the West and local law enforcement officials.

They see Obama’s use of the power to set aside federally owned land for preservation as a threat to security in a region where Mexican drug cartels, human smuggling and illegal immigration are prevalent.

Dona Ana County Sheriff Todd Garrison recalled the times his deputies and federal agents were shot at as they pursued suspected drug smugglers through the area that will now be known as the Organ Mountains-Desert Peaks National Monument. He also talked about the dozens of stolen cars that have been used to ferry drugs along pathways that lead through the desert and past border patrol checkpoints.

“If we have no ability to patrol that area, crime is going to increase,” Garrison said, comparing it to the Organ Pipe National Monument in Arizona, another border reserve where drug smuggling is rife. In 2002, a ranger was fatally shot there in a confrontation with smugglers.

“I wonder how many years it will be before we have to post signs that say ‘Enter at your own risk.’ That’s my concern,” Garrison said.

Officials with U.S. Customs and Border Protection said Wednesday the designation will “in no way limit our ability to perform our important border security mission.”

The campaign by environmentalists, hunters and tourism officials to gain wilderness protection for the Organ Mountains and Desert Peaks has dragged on for a decade, with numerous versions introduced by members New Mexico’s congressional delegation over the years.

New Mexico Sens. Tom Udall and Martin Heinrich, both Democrats, had proposed legislation to protect the region. Republican Rep. Steve Pearce, whose congressional district includes the area, proposed the designation for just 55,000 acres and would have allowed law enforcement a buffer zone.

But the president’s action, using his authority under the Antiquities Act, established much of the area as wilderness, making access more limited.

U.S. Rep. Rob Bishop, R-Utah, had asked Obama to refrain from designating the monument so that Congress through the legislation could address any border security concerns.

“His decision stands and now we have to go back in and try and fix it. That is just a backward way of trying to have good government,” Bishop said.

Supporters of the monument argue that setting aside the area could generate $7.4 million in new economic activity from visitors and business opportunities. They also say the designation could lead to more federal funding and staffing for the Bureau of Land Management and the Border Patrol to enforce the rules that come along with the designation.