Renner estimated that sales dropped 15 percent from last year. He speculated that some consumers may have backed off when they heard rumors of rising interest rates.
MVA spokesman James Lang said the association compiles its report from figures provided by dealerships.
The 23.8 percent dive in sales was high compared to the rest of the year, according to the MVA. January showed a 9.2 percent decrease and February's 6.3 percent.
March and April showed increases of 14.5 percent and 5.9 percent, according to the MVA.
Sales in Hagerstown were reported to be more stable.
"In our particular situation, we have not experienced the kind of weak sales that the MVA has reported," said Ed Zayas, general manager of Hoffman Automotive.
May sales compared to last year were "about the same," he said.
Central Motors of Hagerstown reported a decline, but not nearly as steep as 23.8 percent.
Purchase rates vary statewide because unlike other state residents, consumers here opt to buy sport utility vehicles and trucks over new cars, said Charlie Benson, general sales manager for Hagerstown Ford.
"In this area, (new-car sales) probably are low because truck sales are so strong in the Tri-State area," Benson said. "But in the inner city, they're probably not so low."
On the other hand, Hagerstown Honda owner Paul Ritchie said Honda sales rose 6 percent, pointing out that different brands often do better business depending on the time of year and their latest products.
To help explain this year's overall decline, however, he said certain incentive packages offered last year to attract customers were scrapped this year.
"I wish I did know what caused this," Renner said. "May is usually a great month for sales."