WASHINGTON (AP) — The State Department says it is adding 12 countries to an expanding list of nations whose citizens must post bonds of up to $15,000 to apply for U.S. visas.

Effective April 2, passport holders from Cambodia, Ethiopia, Georgia, Grenada, Lesotho, Mauritius, Mongolia, Mozambique, Nicaragua, Papua New Guinea, Seychelles and Tunisia will be required to pay the bond, which is refunded if the visa application is denied or, if granted, the person adheres to the terms of the visa.

That's according to a notice posted to the State Department website on Wednesday.

After April 2, there will be 50 countries whose citizens are subject to the requirement, which was rolled out by the Trump administration last year as it cracked down on visa overstays and more broadly moved to curtail illegal migration.

Under the program, visa applicants from designated countries, many of which are in Africa, which have high overstay rates, have to post bonds of $5,000, $10,000 or $15,000 depending on their circumstances and the discretion of the consular officer processing the application.

"The visa bond program has already proven effective at drastically reducing the number of visa recipients who overstay their visas and illegally remain in the United States,” the department said, adding that almost 97% of the nearly 1,000 people to have posted the bond had not overstayed their visa.

The full list of countries is here.