U.S. Citizenship and Immigration Services is tightening the rules governing how immigrants already in the United States can obtain green cards, a change that could require more applicants to complete the process abroad through consular processing.

Under a policy memorandum issued last week, the agency said it will generally reserve “in-country” green card approvals, known as adjustment of status, for “extraordinary circumstances.” The shift could significantly affect a process used by hundreds of thousands of applicants each year.