A public interest group says as many as 900 colleges are pushing students into payment cards that carry hefty costs, and sometimes even to access students financial aid money, according to a report by the Associated Press.

The U.S. public interest research group Higher Education Fund says colleges and banks often make deals allowing both entities to rake in millions from the fees, according to AP. The report says some of the fees appear to violate federal law. One of the companies highlighted in this report is Higher One.

The report says more than 9 million people attend schools that have deals with financial companies.

The fees add to the plethora of debt many higher-education students are taking on. U.S. student debt tops $1 trillion and has surpassed credit cards as the biggest source of unsecured debt.

Higher One founder and Chief Operating Officer Miles Lasater told AP that the company completely abides by government rules.

Fees are everywhere: According to its website, if an account is overdrawn for more than 45 days, that's $50; it's $10 if the student refrains from using the account for six months, and $29 to $38 for overdrawing an account with a recurring bill payment.

Higher One has agreements with 520 companies that enroll more than 4.3 million students, according to public filings and the U.S. PIRG report. Wells Fargo and U.S. Bank combined have deals with schools that enroll 3.7 million, the report says.

Programs like Higher One's shift the cost of handing out financial aid money from universities, which no longer have to print and mail checks, to fee-paying students, Rich Williams, the report's lead author, told AP.

Students can opt out of the programs and choose direct deposit or paper checks to receive their college aid, but few do.

Campus card deals are popular in part because of recent litigation that allows banks to generate profits from students.

It used to be, students who had no way of repaying credit cards were banned from having them. Also, colleges were forced to disclose deals with credit card companies; promotion, such as offering students free gifts just for obtaining a credit card, was unconventional.

Now, banks are extending federal aid to students and higher-cost private loans. The recession forced states to slash higher education budgets, and now companies such as Higher One, Wells Fargo and U.S. Bank are assuming the costs and hassle of handling out student aid funds, and paying for the privilege.