Sen. Jeff Sessions (R-AL) expressed outrage at the Obama administration’s enforcement of immigration visa violators Wednesday following the release of data revealing half a million foreign nationals overstayed their visas last fiscal year.

“Visa expiration dates have become optional,” Sessions said in a statement. “The Administration does not believe that violating the terms of your visa should result in deportation.”

According to the Department of Homeland Security report, which was limited to foreigners who came to the U.S. as visitors for business or pleasure via sea or air ports, 527,127 foreign nationals illegally remained in the U.S. beyond the expiration of their visas last year.

“What we are witnessing is tantamount to an open border. Millions are free to come on temporary visas and no one is required to leave,” Sessions, the chairman of the Subcommittee on Immigration and the National Interest, added.

As Sessions noted, thousands of foreigners who overstayed their visas were from high-risk, terrorist-producing nations, including 56 visa overstays from Libya, 219 from Afghanistan, 219 from Yemen, 440 from Syria, 564 from Iran, 681 from Iraq, 922 from Indonesia, 1,147 from Bangladesh, and 1,435 from Pakistan.

“This long-awaited report from the Department of Homeland Security demonstrates that we are in the midst of a national immigration crisis,” Sessions said, noting that the report only looked at a select group of immigrants — tourists and travelers on business — entering via sea and air ports.

Sessions predicted that the true, total number of visa overstays is much greater than what DHS reported.

“These figures do not include any foreign students or any other foreign worker programs such as the H-1B, the L-1, the H-2B and many, many more,” he said. “Nor does it include those who arrived through land ports, thus millions who came on border crossing cards are excluded. And, because this report was only generated using biographic data, and not biometric data, the true number of overstays is likely much higher.

Sessions’ committee is slated to hold a hearing on the biometric entry/exit system later Wednesday.