A University of Florida law professor’s analysis of how “payday loan” companies cluster near military bases provided ammo for those supporting a new federal law protecting soldiers and their families from predatory lenders.

Christopher L. Peterson, an associate professor in UF’s Levin College of Law, along with a geography professor at California State University, mapped payday loan locations in 20 states, including 109 military bases. They found that ZIP codes near military bases had higher numbers of payday lenders than non-military ZIPs with similar demographics. In Florida, ZIP 32210 — adjacent to the Jacksonville Naval Air Station — had the highest number of payday lenders anywhere the state. “That,” says Peterson, “is no coincidence.”

Payday loans are high-interest loans that some use to manage living from paycheck to paycheck. Peterson says junior enlisted personnel make good targets for the loans because they have low salaries and little experience managing money. Meanwhile, non-payment of debt could threaten a soldier’s rank and security clearance, so lenders are confident they’ll be repaid.

The Defense Department used Peterson’s report to bolster the case it’s been trying to make against the payday industry. Testifying before Congress on a bill to prevent predatory lending to servicemen and women, Defense Department officials estimated 225,000 service members, or 17% of the military, use the loans. Financial problems related to the loans are so prevalent, according to the DoD, that they threaten the nation’s military preparedness.

A typical payday lender may give a borrower $100 in exchange for a $115 check dated two weeks later. In what’s known as a “rollover,” if the borrower doesn’t have enough money in the bank when the loan comes due, he refinances by borrowing more on the same terms. A typical lender charges around $17 to $18 for a two-week loan of $100, Peterson says, roughly equivalent to a 450% annual interest rate.

Peterson, author of “Taming the Sharks: Towards a Cure for the High Cost Credit Market,” has studied the history of credit back to ancient times and says that for most of the 20th century America didn’t tolerate triple-digit interest. A gradual erosion of interest-rate caps began in the late 1970s, and the payday loan industry has taken off over the past 10 to 15 years. “This is a recent resurgence of an ancient business,” Peterson says, “but it only exists if governments and communities allow it to exist.”

A few weeks after Peterson testified before the Senate Banking, Housing and Urban Affairs Committee, Congress passed legislation prohibiting lenders from imposing an interest rate of more than 36% on loans to members of the armed forces or their dependents. Peterson calls it “the most consumer-friendly legislation passed in a generation,” but he says the protections should be spread to all citizens, not only soldiers. “If a business can’t make a profit at 36%, chances are they shouldn’t make the loan in the first place.”

Twelve states prohibit triple-digit rates on payday loans. Florida is not one of them.