Citing the Immigration and Nationality Act, ICE officials said the agency has the right to impose civil fines, up to $799 a day, on undocumented immigrants who have been ordered removed, or who have failed to leave the country. Officials said the agency began issuing such notices in December, though it was not clear on Thursday how many had been sent.

“ICE is committed to using various enforcement methods — including arrest, detention, technological monitoring and financial penalties — to enforce U.S. immigration law and maintain the integrity of legal orders issued by judges,” said Carol Danko, an agency spokeswoman.

Earlier this week, President Trump — who signed an executive order shortly after his inauguration that called on the Department of Homeland Security to collect all fines and penalties from anyone who had entered the country illegally — said that his administration would begin immigration raids after July 4.

This week’s batch of letters caught pastors and immigration activists by surprise, as houses of worship, like hospitals and schools, have generally been excluded from raids.

At St. Andrew’s Presbyterian Church in Austin, Tex., Hilda Ramirez Mendez also received a notice this week that she was under final order of removal and would be fined $303,620. She has been living for a while at the church with her 13-year-old son, whose special immigrant juvenile status application is pending. She was denied asylum in 2015, and although ICE initially allowed her to stay, her deferred action status was not extended in March, said her lawyer, Stephanie Taylor.