The Target boycott cost more than anyone expected — and the CEO was blindsided (TGT)

Target triggered a nationwide boycott last year with a single blog post — and it turns out the message was as big of a shock to the company's CEO as it was to some shoppers.

The blog post, published in April 2016, publicized a policy that said transgender customers were welcome to use the bathroom or fitting room that matched their gender identity.

"Everyone deserves to feel like they belong," the post said. "And you'll always be accepted, respected and welcomed at Target."

Target CEO Brian Cornell never approved the post and found out about it only after it was published, according to The Wall Street Journal.

He later told colleagues that he wouldn't have approved the decision to "flaunt" the policy and that the backlash was "self-inflicted," The Journal reported.

The boycott cost the company millions in lost sales and added expenses. Shopper traffic and same-store sales started sliding for the first time in years after the blog post, and the company was forced to spend $20 million installing single-occupancy bathrooms in all its stores to give critics of the policy more privacy.

Critics of the policy said it opened the door for sexual predators to victimize women and children inside the retailer's bathrooms, and more than 1.4 million people signed a pledge to stop shopping at Target unless it reversed the policy.

Sales fell nearly 6% in the three quarters after the post compared with the same period last year, and same-store sales have dropped every quarter since the post.

Cornell didn't approve the post, according to The Journal, but he supported the policy in interviews after it was published.

"We took a stance, and we are going to continue to embrace our belief of diversity and inclusion," Cornell said in an interview with CNBC in May.

In the past, even the most widespread calls for company boycotts have tended to blow over within a matter of weeks or months.

Chick-fil-A, for example, faced a nationwide boycott in 2012 after Dan Cathy, the son of Chick-fil-A's founder, S. Truett Cathy, set off a fury among supporters of equal rights for gay people when he told Baptist Press that the company was "guilty as charged" for backing "the biblical definition of the family unit."

Reports then emerged detailing Chick-fil-A's many charitable donations to organizations opposed to same-sex marriage.

Despite the backlash, Chick-fil-A's sales increased 14% in 2012.