Immigration Customs Enforcement released hundreds of detainees last week and placed them on monitoring systems throughout the country.
"Who within the ICE chain of command has the authority to decide to release a particular criminal alien and what is the written policy limiting the officer's discretion?" McCain wrote in a letter to Homeland Security Secretary Janet Napolitano, The Hill reported.
"What plans are in place to ensure illegal aliens are being detained and we do not return to the days of Border Patrol 'catch and release'?" McCain asked in the letter, which was released Friday.
Napolitano and the White House have said ICE officials made the decision to release the undocumented immigrants in an effort to manage the agency's resources when automatic government spending cuts, known as the sequester, went into effect March 1.
Republicans in Congress have said they plan to press for more details on the ICE decision.
ICE has said it has no plans to release any more undocumented immigrants into the monitoring program.
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