A commenter on the Whole Foods forum, identified only by his handle, "PracticePreach," wrote, "It is an absolute slap in the face to the millions of progressive-minded consumers that have made [Whole Foods] what it is today."
"You should know who butters your hearth-baked bread, John," wrote the commenter. "Last time I checked it wasn't the insurance industry conservatives who made you a millionaire a hundred times over."
While Mackey reduced his annual salary to one dollar in 2007, after explaining to employees he was "no longer interested in working for money," Mackey is still the head of the 10th largest food and drug store in the U.S.
Whole Foods Market Inc. reported that sales for the last quarter rose by 2 percent to $1.878 billion. It is consistently ranked a Fortune 500 company.
And not all Whole Foods customers were upset by Mackey's op-ed.
Many posted online that they agreed with his message and would try to shop at the chain more often.
Frank Federer wrote ABCNews.com, expressing fatigue with the knee-jerk reaction of other shoppers.
"You can count me as one vote FOR Whole Foods' CEO," wrote Federer. "At a time when most folks are more inclined toward rancor than discussion of facts, I applaud John Mackey."
Despite his financial success, this is not the first time Mackey has become fodder for criticism. In 2007, it was discovered that Mackey had been using a pseudonym to post blogs lambasting Whole Foods' competitor, Wild Oats Market, and questioning the worth of the company's stock.
The postings were made public when Mackey announced his desire to buy Wild Oats Market, and a lawsuit was filed by the Federal Trade Commission over concerns that the purchase would violate antitrust laws.
The FTC eventually let the sale go through, provided that Mackey sold 31 of the Wild Oats stores, and the Securities and Exchange Commission, which had launched an investigation into the online postings, did not press charges.
Libba Letton, a Whole Foods spokeswoman, told ABCNews.com that Mackey was unavailable for an interview and said that the op-ed "stands on its own." Letton offered no further comment regarding customers' threats to boycott the store.
According to Robert Passikoff, the founder of Brand Keys, a N.Y.-based consulting firm, what a CEO says or does can often have a direct impact on consumers' pocketbooks.
"You can have a tremendous effect as a CEO, but it's a double-edge sword in that you'll have people who will support your position and feel better about your brand because of what you say," said Passikoff. "But equally so, you'll have people who think you're crazy and because they can't take it out on you, the CEO, they'll take it out on the company."
It is the risk of losing customers, said Passikoff, which more often than not leads CEOs to keep their mouths shut, at least when it comes to polarizing issues such as health care.
Tom Monaghan, the founder of Domino's Pizza who was outspoken in the pro-life movement, ostracized many of his consumers who weren't sure how much of the money he earned making pizza was then going to support the pro-life movement.
Lynn Upshaw, a brand marketing consultant at Upshaw Brand Consulting in Kentfield, Calif., said that more often it is the actions of an entire company, and not just of a CEO, that lead to boycotting by consumers.