Sen. Susan Collins has sent a letter to the president and CEO of Progressive Corp. asking her to justify the company’s attempts to raise auto insurance premiums for seniors in Maine.

“I was greatly concerned to learn that Progressive … has been seeking approval to indiscriminately charge higher automobile insurance premiums based solely on when existing policyholders reach certain ages,” the Maine Republican begins her letter to Tricia Griffith, Progressive’s top executive.

Progressive is seeking state approval for rate changes that would allow the company to charge older Mainers higher auto insurance premiums based solely on their age. The proposal by the Ohio-based company would apply only to new customers in Maine, according to documents filed with the state Department of Professional and Financial Regulation’s Bureau of Insurance.

A hypothetical example that Progressive provided to the bureau shows a 65-year-old being charged 6 percent more than a 64-year-old based solely on the customer having reached age 65.

Increasing rates for seniors based on their age alone would be a major departure from the way most insurance companies operate nationwide and in Maine, which has a population that leads the nation in average age. Traditionally, healthy drivers with flawless driving records see their premiums decrease as they age.

Progressive spokesman Jeff Sibel said via email that the company has not proposed raising seniors’ rates in Maine, and that it is only seeking clarification from the bureau on how it can more accurately price its customers under Maine law.

“As an industry practice, rates are developed using well-accepted actuarial principles that consider numerous factors relating to a person’s risk of loss,” Sibel said. “A major factor is loss experience, which Progressive and industry data clearly shows deteriorates as people grow older.”

Sibel said Progressive intends to respond to Collins’ questions about the company’s reasons for requesting a rate hearing about older drivers in Maine.

In her letter, Collins points out that Progressive’s proposal in Maine ultimately could have consequences for all seniors nationwide. Collins is chairwoman of the Senate Special Committee on Aging.

“There are presently 36 million American drivers age 65 or over, and every day roughly 10,000 more join their ranks,” the letter says. “For most of those seniors, their own automobile is essential to remaining active and engaged, especially those who by choice or necessity remain in the workforce.”

Collins’ letter goes on to note that research shows older drivers are less likely than younger drivers to be involved in crashes, and that they are also less likely to cause the deaths of other vehicle occupants, pedestrians, bicyclists and motorcyclists.

“In light of this data, I request justification of the proposed change,” the letter says. “Further, I would like to know whether Progressive is pursuing similar rate filings in (other) states, and whether Progressive believes that such policy is permissible under federal law.”

Earlier this week, the House chairman of the Maine Legislature’s Insurance and Financial Services Committee submitted legislation that would prohibit insurance companies from charging older Mainers higher premiums based solely on their age.

Rep. Henry Beck, a Democrat who represents parts of Waterville and Oakland, submitted to the Revisor’s Office a proposed amendment to the Maine Insurance Code in response to Progressive’s bid to get permission from the state Bureau of Insurance to impose age-based increases on older drivers.

Current Maine law prohibits insurers from boosting existing customers’ premiums as they age, but Beck said it isn’t clear whether the existing statute applies to new insurance consumers. In a June 10 decision denying Progressive’s request to raise rates for existing customers as they age, the bureau agreed that the rules regarding new customers are somewhat vague.

After denying the company’s initial rate filing and closing the case, the bureau agreed to reopen it for further discussion at Progressive’s request. The discussion would pertain only to the possibility of age-based ratings for new customers, the bureau said.

Bureau representatives said state Superintendent of Insurance Eric Cioppa would not be allowed to comment on Progressive’s rate filing until the case is closed. A meeting with Progressive has been scheduled for Aug. 16.

The request drew opposition from aging advocates such as AARP and Jessica Maurer, the state director of the Association of Area Agencies on Aging.

“To randomly suggest that 65 is a time when you’re going to get into more accidents … it’s a very random and arbitrary suggestion,” Maurer said.

About 14 percent of Maine drivers had policies through Progressive and its affiliates in 2014, according to the most recent Bureau of Insurance figures.

One factor that could be driving the company’s request is Maine’s higher-than-average rate of fatal accidents involving drivers 65 and older. According to the National Highway Traffic Safety Administration, Maine led the nation in 2012 and 2013 with the highest share of older drivers involved in fatal accidents. In 2012, the share of fatal accidents involving drivers 65 and older in the U.S. was 12.7 percent. In Maine, it was 18.6 percent. In 2013, the share nationally was 13.3 percent, and in Maine it was 20.6 percent.

Overall, Mainers paid $758 million in auto insurance premiums in 2014, according to the National Association of Insurance Commissioners.