PHOENIX—Migrants who are caught crossing the border illegally for the first time are now facing criminal charges in federal court in Arizona as the Trump administration steps up efforts to deter illegal immigration.

Until recently, first-time offenders were deported instead of being criminally prosecuted.

That changed as of June in the Tucson Sector, which includes most of Arizona’s border with Mexico, the agency said in a news release on Thursday. The new program has led to 565 prosecutions.

The illegal immigrants are charged with misdemeanors and tried in federal court under Operation Streamline, a 12-year-old initiative in which the migrants are charged, enter pleas and are sentenced within a few minutes in large groups.

A recent docket for Operation Streamline, which takes place in Tucson several times a week, shows that 58 immigrants were tried on Thursday. About 35 were first-time offenders who were charged with improper entry. The rest were migrants who have previously been caught at the border and were charged with illegal re-entry.