Mexico's immigration agency says it will subject officials to psychological, drug and lie detector tests in an effort to combat corruption.
National Immigration Institute Commissioner Salvador Beltran del Rio said 40 agents are now under investigation for human rights and other abuses. He added in a Sunday news conference that the agency will begin rotating officers in key regions.
The steps follow Thursday's firing of seven top immigration officials in areas where migrants have been victimized.
Mass graves containing 183 bodies were discovered last month in Tamaulipas state, bordering Texas. Some of the victims are believed to be migrants.