China's President Xi Jinping. (Jason Lee/Reuters)

In early March, Wen Yunchao, a New York-based blogger, spotted something unusual in his email: a letter urging China's president to resign.

The letter, signed "loyal Communist Party members," blasts President Xi Jinping for "abandoning the principle of collective leadership," concentrating power in his own hands and "indulging" flatterers. It claims to be written out of consideration for Xi and his family's "personal safety."

Wen, who also uses the name Bei Feng, soon heard the letter was live on the Web. He did a quick search and found the text on Wujie, a government-linked website, he said. He tweeted the link.

That, it seems, was a dangerous move.

On Friday, Wen went public with the news that his brother and parents, who live in Guangdong province, in southern China, were this week "taken away" by Chinese authorities. He heard the news from his sister-in-law, he said, who would not disclose what the security personnel told her, or where they were being held.

Their detention appears to be linked to the letter: Earlier this month, his father and brother told him they were visited by local officials. They wanted to know about Wen's alleged involvement in "spreading" the document. Wen maintains he merely tweeted the news. He has not been directly contacted by Chinese police, he said.

Wen's relatives are not the only people caught in a widening crackdown on people believed, rightly or wrongly, to be linked to the case.

On March 15, a Chinese journalist named Jia Jia went missing on his way to a flight from Beijing to Hong Kong. Jia's lawyer has said his client did not write the letter. Sources identified as friends of the writer told various media that Jia may have been nabbed for telling Ouyang Hongliang, a Wujie editor, that the letter was online. (With Jia being held incommunicado, that detail is impossible to confirm.)

The BBC on Friday reported that as many as 16 Wujie employees have been "taken away" by Chinese authorities. Their report cites an unnamed source within the organization who said that six of the 16 worked in the editorial department, and 10 were on the tech side.

The fact that 10 tech staff members were reportedly targeted could lend credence to the theory -- and it's just a theory at this point -- that the letter was published on the site by a hacker, or by some sort of "trawling" software that pulls and republishes content. The Post could not independently confirm the BBC's account; Wujie's phones went unanswered Friday.

It's no surprise China's vast security apparatus is acting on the case. Since coming to power in 2012, Xi has arrested government critics and reined in the Party-controlled press -- a tactic that seems to be riling some quarters.

The March 4 letter was posted just weeks after Xi toured state media offices in Beijing, asking the press for absolutely loyalty. A prominent tycoon-turned-blogger, Ren Zhiqiang, responded by publicly questioning Xi's stance.

“When did the ‘People’s Government’ turn into the ‘Party’s Government?’ ” he asked. (He was later denounced by the Party-controlled press.)

Soon after, Caixin, one of China's most respected magazines, lashed out at the authorities for censoring an article in which a Shanghai academic suggested the government ought to listen to competing views.

In an English-language follow-up headlined “Story about Adviser’s Free Speech Comments Removed from Caixin Website,” the same academic, Jiang Hong, went on the record about what he called a “terrible and bewildering” act of censorship.

“I examined [the article] in all respects, but I couldn’t see anything illegal,” he told Caixin.

The detention of Wen's family members is a reminder that doing something illegal is not necessarily a requirement when it comes to being "taken away." These days, suspicion, or relation, is enough.

Xu Yangjingjing contributed to this story from Beijing.

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