Twenty-percent sales growth a year.

That is what Stock Advisor recommendation Whole Foods Market's (NASDAQ:WFMI) founder, chairman, and CEO, John Mackey, is targeting so the company can reach its goal of $12 billion in annual sales in 2010. So far, the company is on track, growing revenue last quarter by 20.9%, as reported May 3 in the earnings release for fiscal 2006's second quarter. It also reported $0.37 in earnings per share, beating estimates by $0.02; it had missed earnings estimates the previous two quarters.

That sales growth comes from double-digit same-store sales growth (the five-year average is 11%) and opening new locations (the five-year average is increasing square footage by 15%). So far this strategy of increasing both has worked. The company promotes heavily that shopping at Whole Foods represents a lifestyle choice of eating healthier food. It relies on people being committed to that choice, because organic food in general is more expensive than what one can buy in "regular" supermarkets, such as Safeway (NYSE:SWY) or Kroger (NYSE:KR). But those companies are recognizing the large margins and potentially huge market for organic food. They're expanding their organic food sections, improving the look, layout, and size. Whole Foods is not concerned, having seen and weathered such initiatives in the past.

Now, though, there is another competitor entirely. Wal-Mart (NYSE:WMT) has entered the fray, offering organic food at its grocery stores. So far the competition is low-level, with only about 1,700 products offered compared with more than 30,000 at Whole Foods. However, Wal-Mart is the world expert at supply-chain management, something key to its offering thousands of products at low prices. This presents some potential problems as well as opportunities for Whole Foods.

First, Wal-Mart should be able to get lower prices from suppliers. This could squeeze the organic farmers who also supply Whole Foods. Those farmers in turn could raise their prices to Whole Foods to try to rebalance their own costs. While that may not happen -- Whole Foods has a bit of pricing power itself with more than 180 stores -- the alternative might be that the organic farmer goes out of business.

Second, with a potentially major seller entering the picture, more farmers might be drawn to switch at least part of their operations over to organic growing. Thus, the number of suppliers would increase, benefiting both Wal-Mart and Whole Foods, as well as other grocery chains. Based on Mackey's remarks during the conference call, this seems to be what Whole Foods is expecting to happen.

Third, as the self-declared low-cost provider of everything from apples to xylophones (OK, maybe not those, but you get the idea), Wal-Mart could be trying to break the mold that Whole Foods depends on -- the idea that organic food is a lifestyle choice that people are willing to pay up for. On the whole, organic food is more expensive than "regular" food. However, if Wal-Mart can drive the price down, customers may not be willing to pay the extra premium to stay committed to that lifestyle.

Finally, Wal-Mart's distribution system supplies its stores with what is needed as it is needed. If it offers organic food in a big way, one could imagine that Whole Foods would have to respond by increasing and streamlining its own distribution system. This would cut into cash needed for store expansion, which would slow down that part of its growth formula. To date, all of its growth has been funded by internal cash flow. If some of that has to be diverted elsewhere, the company would face the choice of slowing down the growth plan or raising cash elsewhere. Total debt is virtually non-existent, so Whole Foods has some room there.

Even though Mackey downplayed the potential problems represented by Wal-Mart in Wednesday's earnings call, the Foolish investor needs to be aware of them. A competitor on the scale of Wal-Mart is not the same as one on the scale of Kroger or Safeway.

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Fool contributor Jim Mueller doesn't buy organic and doesn't own shares in any company mentioned. The Motley Fool is investors writing for investors.