Because of a federal budget cut, thousands of low-income students across the nation may not be able to afford the fees for their Advanced Placement exams this spring — exams that could save them thousands of dollars in college tuition.

As part of the federal budget agreement last December, Congress cut federal financing for programs that offer advanced high school courses to slightly under $27 million, from $43 million the previous year, with only about $20 million to be used to subsidize low-income students’ exam fees. So, in recent weeks, state education officials have been notifying high schools that low-income students, who have for decades been eligible for fee waivers, will have to pay $15 for each of the first three exams they take, and $53 per exam for any beyond that.

A.P. exams, given in May, cost $87 apiece, and many schools are now in the process of collecting registrations and fees.

At Classical High School in Providence, R.I., where 70 percent of the students qualify for free or reduced-price meals, Louis Toro, the Advanced Placement coordinator, said that some students who had expected to take four or five A.P. exams were cutting back to three.