The federal government wants U.S. residents with green cards, parolees and some Canadians to have their fingerprints checked every time they re-enter the U.S. by air or sea.

The new security checks announced Thursday by the Department of Homeland Security are part of the so-called US-VISIT program, which requires border-crossing documents to include a digital photograph and two fingerprints. The program, which currently has 61 million people enrolled from countries except Canada and Mexico, is being slowly phased in.

"We have a lot more steps along the way," said Bob Mocny, acting director of the US-VISIT program.

Mocny estimates that the new requirement would add 1 million to 1.5 million enrollees. The public may comment on the program until Aug. 28.

The purpose of the program is to screen out criminals and make sure that travel documents aren't forged.

Under US-VISIT, the U.S. government has caught 1,100 criminals at ports of entry, Mocny said.

There are between 8 million and 12 million legal permanent residents — or green-card holders — in the United States. But only a fraction of them travel outside of the country, Mocny said.

Canadians who cross the border to shop, visit or take a holiday or a short business trip won't need to enroll in the program, according to the proposed rule published in the Federal Register.

But some Canadians are subject to stricter border-crossing scrutiny because they work or study in the United States. Those Canadians — including nurses, agricultural workers, students and religious workers — will be required to enroll, but they'll only have their fingerprints checked at land ports if a Customs and Border Protection official questions the validity of their documents, Mocny said.

Canadians such as nurses or students who come to the United States just to shop or visit wouldn't have to enroll in the program. And those who do have to enroll in the program would be admitted like other Canadians when they cross the border to shop or visit.

Everyone who re-enters the U.S. through an airport or seaport will be checked, he said.

The program won't apply to Mexicans coming into the U.S. with a border crossing card.