(Bloomberg) — Progressive Corp., the fourth-largest U.S. autoinsurer, said it will begin increasing rates for some riskycustomers who participate in a program that allows the company toelectronically monitor driving habits.

The decision to lift premiums is a shift for Mayfield Village,Ohio-based Progressive, which previously highlighted how customerscan agree to a rate and then win discounts for safe behavior. ItsSnapshot program rewards customers who drive fewer miles, avoidhard braking and minimize travel from midnight to 4 a.m., accordingto the company's website.

"In our new program that we just began to roll out, we areaffording more customers discounts for their good driving behaviorwhile for the first time, increasing rates for a small number ofdrivers whose driving behavior justifies such rates," the companysaid in its annual report this month.

Chief Executive Officer Glenn Renwick has said Snapshot couldhelp the company encourage safer behavior and retain the mostvaluable customers. He has lamented the reluctance of somepotential customers to sign up for the offering. That unease couldincrease under the new strategy, according to Jonathan Adams andJamie Dranoff of Bloomberg Intelligence.

"This is a key policy shift," they wrote in a report Tuesday."The decision to raise prices for some bad drivers may discouragecustomer acceptance of Snapshot, whose sales grew 28% in 2014."

The program will apply to new customers and is being tested inMissouri, Amanda Lupica, a spokeswoman for Progressive, said in aphone interview. It is likely to roll out in additional states inMay or June, she said.