Budget cuts have hampered the U.S. Border Patrol’s work in its busiest sector on the Southwest border, agents said Friday, with the agency introducing fuel conservation measures in the Rio Grande Valley that have agents patrolling on foot and doubling up in vehicles.

The Border Patrol instituted the changes after the across-the-board government spending cuts known as sequestration. The constraints come as Congress moves deeper into the debate over comprehensive immigration reform and Republican legislators push for stronger border security components as a precursor to any path to citizenship for immigrants who have entered the country illegally.