Jordan's King Abdullah of has endorsed a new media law which critics say will stifle freedom of expression online.
The legislation requires "electronic publications" in Jordan to get a licence from the government.
It also gives the authorities the power to block and censor websites, whose owners will be held responsible for comments posted on them.
Human Rights Watch accused the government of using such legislation to "go after opponents and critics".
Media professionals and ordinary citizens regularly found themselves charged with and convicted of criminal offences related to speech, it said.
In April, the State Security Court military prosecutor detained the editor of the Gerasa News website for trying to "undermine the system of government" after it published an article about the king's alleged intervention in a corruption investigation.
The case remains open but the trial has not yet started.
'Check the truth'
Human Rights Watch said the dangers of the amendments to the Press and Publications Law endorsed on Monday arose from its vague definition of the "electronic publications" which would be affected, the new executive power to block websites, and the unreasonable restrictions on online content, including comments posted by website users.
The legislation's definition of electronic publication is "an electronic site on the internet with a fixed address that offers publication services".
Any that publish "news, investigations, articles, or comments, which have to do with the internal or external affairs of the kingdom" must register with the commerce ministry and get a licence from the culture ministry.
The culture ministry will have the authority to block websites that are either unlicensed or deemed to be in violation of any law, and to close the website's offices without providing a reason or obtaining a court order.
The owner, editor and director of an electronic publication will share the responsibility for comments posted on their website, and be obliged not to publish any "containing information or facts unrelated to the news item or if the truth has not been checked", or if they "violate laws".
"The government has not shown a valid reason for prohibiting user comments that are deemed unrelated to the item that triggered the comment, a prohibition that appears to be arbitrary interference in the right to free expression," HRW said.
"Obliging website managers to check the truth of comments is also not a valid restriction on freedom of speech, which includes the freedom to express unproven statements or even falsehoods."
The Associated Press estimated that about 400 Jordanian websites would be affected by the new law.
The Press and Publications Law and the penal code already criminalise defamation, including libel and slander, including against entities that are not people, such as government institutions, symbols and religions.