Details of a new law issued by China’s supreme court are bound to make loose talkers on Sina Weibo and other social media platforms think twice before speaking freely. The law says that any libelous posts or messages will be considered “severe” breaches of the law if they are visited or clicked on more than 5,000 times or forwarded (or “retweeted,” in Western parlance) more than 500 times. Those found guilty could face up to three years in jail, reports Reuters, citing Chinese state media.

As if that weren’t alarming enough, the threshold for being charged with this crime includes offenses as vague and subjective as “damaging the national image” and “causing adverse international effects.”

The law is the latest attempt to crack down on “black PR firms,” companies that make money from removing unflattering information from the internet. Among other things, black PR firms often target companies, spreading gossip or misinformation about them, and then approaching them for payment in exchange for removing the smear campaign. It’s a big business; as TechinAsia pointed out recently, the Sina Weibo accounts controlled by a huge black PR firm that was just busted had a total audience of 220 million followers.

As Caixin reports, since the campaign against “rumor-mongering” and “spreading false information” picked up in June, Shanghai police have opened more than 380 cases, while Henan police have investigated a whopping 463 cases, making 131 arrests. And it’s not just Sina Weibo; TechinAsia reports that police are also watching Tencent’s WeChat, which is organized mainly around private circles of friends.

But for every big black PR firm bust, authorities also seem to be ensnaring a lot of innocent users of social media.

For example, in late August, a women in Anhui province posted on Sina Weibo that 16 people died in a car accident that had just taken place, when the death toll was only 10. Local police placed her under “administrative detention” for five days as punishment for “spreading rumors.” In another case, a 20-year-old Anhui woman was imprisoned for posting the comment “I heard there was a murder in Louzhuang—is there anyone who knows what actually happened?” on a Baidu discussion board. The post, which was clicked on 1,000 times, counted as “disrupting social order” (link in Chinese).

In late August, a Weibo user stoked online discussion with a post saying that the “five heroes of Langya Mountain”—martyrs in the war against the Japanese who are a source of Communist Party pride—had actually been army deserters who oppressed the local villagers of Langya, and that the latter eventually gave them up to the Japanese. This, determined the local police, “created unhealthy social effects” (link in Chinese). Authorities arrested and held the Weibo user under administrative detention for seven days. Something similar happened with four people who “defamed” the Party mascot, Lei Feng.

The new clarifications have big implications for harmless online chatter. If the posts of an amateur historian or inquisitive citizen garner enough attention, the author could face three years in prison.