The U.S. Department of State announced it is expanding a visa bond requirement for certain travelers, adding 12 countries to the list of nations whose citizens must post refundable security when applying for U.S. visas. In a notice posted to the State Department’s website Wednesday, the department said the bonds would be required for passport holders from Cambodia, Ethiopia, Georgia, Grenada, Lesotho, Mauritius, Mongolia, Mozambique, Nicaragua, Papua New Guinea, Seychelles and Tunisia starting April 2.

The State Department said the bonds will be refunded if a visa application is denied or if, after receiving a visa, the applicant adheres to the terms of the visa. It also said the bond amounts can reach up to $15,000, depending on circumstances and on the discretion of the consular officer handling the application.

Under the program, visa applicants from designated countries—many of which are in Africa and have high overstay rates—have to post bonds in amounts of $5,000, $10,000 or $15,000. The State Department said the bond requirement is part of a broader effort that began rolling out under the Trump administration last year, as it cracked down on visa overstays and moved to curb illegal migration.

The State Department said the visa bond program has “already proven effective” at reducing the number of recipients who overstay and illegally remain in the United States. The department said almost 97% of nearly 1,000 people who posted the bond under the program had not overstayed their visa, adding that the full list of countries is available through a link in the notice.

After April 2, the State Department said there will be 50 countries subject to the bond requirement, expanding further from the list that was introduced earlier last year. MSI previously reported that the Trump administration expanded the visa bond list to 38 countries in early January.