Bloggers and others running online platforms in Tanzania have two weeks to register with the government or face fines and jail time. Rights groups are expressing concern about the measure, which stems from a new law regulating online content.
The new law in Tanzania targets online platforms such as blogs, podcasts and live streaming content, for example via YouTube channels.
The government said it will monitor the platforms for hate speech, obscene content and threats to national security and public order.
Local bloggers fear the oversight will be used to stifle dissent.
Maxence Melo is the co-founder of Jamii forums, a website about corruption in Tanzania. He has been detained several times since 2015, with two formal arrests.
"We have been a lot of pressure from our government in the past years because authorities wanted to know our whistleblowers, and we said we cannot do this," said Melo. "And most of the whistleblowers were people helping to reveal some misconduct in the government. As we speak, we are facing three trials, and all of them are about revealing our sources of our stories."
Tanzania's government spokesman declined VOA's request for an interview.
On Friday, the Tanzania communication regulatory authority said the owners of online platforms must pay about $900 to get a license. The state agency also said it would use suspensions to force the removal of content it deems in violation of the law.
Those who fail to comply with the new regulations could face fines and up to a year in jail.
Reporters Without Borders has slammed the license fee as "exorbitant" and called the new law "the latest blow to free speech in Tanzania."
Since taking office in 2015, President John Magufuli has cracked down on a range of issues, including corruption, tardiness among civil servants, and criticism of his government.
Newspapers seen as critical of his administration have been shut down or had their licenses suspended.In February, two opposition politicians were jailed for allegedly insulting the president.
Henry Maina is the East Africa regional director for Article 19, a global NGO that promotes freedom of expression and information worldwide.
"Tanzanians are beginning to organize themselves online, and so here is a clear measure of a state policy to try and close down civic space," said Maina. "And in so doing, they are not only closing down civic space, but they are closing down virtual space so that Tanzanians cannot organize."
Maina points to a regional trend. Countries including Uganda, Democratic Republic of Congo and Ethiopia have cut the internet or restricted access to certain social media sites during times of unrest.
Rights groups such as Article 19 urge restraint.
"There is a big discussion globally on how to regulate social media, but that must not be equated to criminalizing social media. Yes, regulation may be required," but only for several purposes, Maina said, adding those would include protecting national security, public morality, public health and individuals' reputations. "Any other reason that a state may throw up as a reason for regulating or controlling social media in itself will be a violation of human rights."
In Tanzania, bloggers and other administrators of online platforms have until May 5 to register. Their licenses will then come up for renewal, for a fee, every three years.
Khaleed Abubakar contributed reporting for this story from Dar es Salaam, Tanzania.