Shares of O'Reilly Automotive Inc (ORLY - Get Report) are plunging Wednesday, down 19%, after the company warned that its sales were not as robust as investors had been hoping for.

Previously expecting comparable-store sales results of 3% to 5% for the quarter, management now expects comps to come with growth of 1.7%. This is a "tremendous disappointment" to the market, TheStreet's Jim Cramer, manager of the Action Alerts PLUS charitable trust portfolio, said on CNBC's "Mad Dash" segment.

What makes the warning even more disappointing is that O'Reilly seemed to have good momentum coming into the quarter, Cramer added.

He also pointed out that the entire sector is struggling as well, with companies like AutoZone, Inc. (AZO) and Advanced Auto Parts, Inc. (AAP - Get Report) down respectively 7.5% and 12% on Wednesday.

The struggles are deeper than one day, though. In fact, O'Reilly shares are down 34% on the year, roughly in-line with the performances of AutoZone and Advanced Auto, which are down respectively 33% and 38% on the year.

While these names are down big over the past year, Cramer was quick to point out that the long-term gains are still big. For instance, O'Reilly shares are still up roughly 120% over the last five years.

He reasoned that there could be mergers in the future for this industry, as a mix of competition and location count have changed the retail landscape. Of course, look no further than Amazon (AMZN - Get Report) when it comes to disrupting retail, although Cramer said he takes the Amazon threat less seriously than other investors when it comes to auto parts.

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At the time of publication, Jim Cramer's Action Alerts PLUS had no position in any companies mentioned.