Weakness in new-vehicle retail sales experienced during the first half of June continued at an accelerated rate through the remainder of the month, pulling the retail selling rate below 8.5 million units, according to J.D. Power and Associates, which gathers real-time transaction data from more than 8,900 retail franchisees throughout the United States.

In the week leading up to the close of the month, June new-vehicle retail sales were down 5 percent compared with one-year ago. As fleet sales are not expected to change significantly, the total seasonally adjusted annualized rate may come in well below the 10.9 million units previously expected.

"It appears that the volatility in the stock market and downbeat economic reports have caused a decrease in consumer confidence, leading to a self-fulfilling prophecy," said Jeff Schuster, executive director of global forecasting at J.D. Power and Associates. "Consumers are clearly hunkering down in light of the current environment, waiting for signs of a renewed recovery."