CNBC reported that U.S. auto sales fell in August, signaling what some major automakers believe is the beginning of a long-expected sales decline or, at best, an industry sales plateau. This sales decline could spark a shift to better customer incentives, slowed production or more fleet sales.

The biggest U.S. automakers, General Motors and Ford, even reported declining sales following a surprisingly strong July.

Ford Chief Economist Bryan Bezold said sales have hit a plateau after steadily rising following the 2008-2009 recession. The auto industry outperformed the overall U.S. economy in those years largely due to pent-up demand that has now played out, he said.

Wall Street has pressured automaker shares all year as expectations of falling sales were widely expected at some point this year.

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