U.S. immigration officials are planning a month-long series of raids in May and June to deport hundreds of Central American mothers and children found to have entered the country illegally, according to sources and an internal document seen by Reuters.

The operation would likely be the largest deportation sweep targeting immigrant families by the administration of President Barack Obama this year after a similar drive over two days in January that focused on Georgia, Texas, and North Carolina.

Those raids, which resulted in the detention of 121 people, mostly women and children, sparked an outcry from immigration advocates and criticism from some Democrats, including the party’s presidential election frontrunner Hillary Clinton.

The exact dates of the latest series of raids were not known and the details of the operation could change.

Immigration Raid Details