International media freedom groups have criticised Jacobson’s arrest, saying it criminalises journalism in a country which has a sinking reputation for freedom of information.

Andreas Harsono, a researcher at Human Rights Watch Indonesia who is familiar with Jacobson and his work, said the case was an administrative matter and should not warrant jail time.

“Journalism is not a crime,” Harsono said. “We need to urge the immigration authorities to dismiss this case.”

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Jacobson was arrested on Tuesday in Palangkaraya, the capital of Central Kalimantan on the island of Borneo, where he had gone to attend a meeting between a local indigenous group and provincial parliamentarians.

He had previously been detained there for several weeks while immigration authorities looked into his case.

Mongabay founder Rhett Butler said Jacobson was not in Palangkaraya to do any reporting, and that the organisation was working hard to secure his release from a detention centre where he was sharing a cell with five other prisoners.

“I am surprised immigration officials have taken such a punitive action against Philip for what is an administrative matter,” Butler said.

Jacobson’s lawyer, Aryo Nugroho, the head of Indonesian Legal Aid in Palangkaraya, said the case hinged on his arrival in Indonesia on a business visa rather than a journalist visa, according to the New York Times.

However, there are concerns Jacobson came under scrutiny for his reporting, which included the exposure of corporate activities violating environmental regulations and investigations into the environmental track record of Indonesia’s President Joko Widodo.

Immigration spokesperson Muhammad Syukran told Agence France-Presse the case was only an issue of immigration law enforcement, and denied that the authorities had an issue with Jacobson’s work. Syukran did not respond to further requests for comment.

Daniel Bastard, the Asia-Pacific head for Reporters Without Borders, criticised Jacobson’s arrest as “totally disproportionate”, and said it amounted to intimidation.

The organisation ranks Indonesia 124th out of 180 in its world press freedom index, citing media restrictions in the restive eastern province of West Papua, where authorities also blocked internet access during protests last year.

Harsono at Human Rights Watch said Jacobson’s case would not do anything to improve the country’s tanking press freedom ratings.

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Indonesia’s laws were problematic because the definition of what constituted journalism was so loose, he said. “The criteria is so wide, and meanwhile the discipline of journalism is also very wide. You can be a doctor or an architect or an engineer and still write, or keep a blog.”

Harsono said the approval process for getting a journalist visa in Indonesia was “filled with red tape”, requiring journalists to submit their plans for sourcing and meetings to authorities for approval.

The Indigenous Peoples Alliance of the Archipelago – Indonesia’s largest indigenous rights group, whose meeting with parliamentarians Jacobson had attended before his arrest – said the case was a threat to press freedom, democracy and human rights in the country.

Shawn Crispin, senior Southeast Asia representative for the Committee to Protect Journalists, said the longer Jacobson was held, “the more damage Indonesia does to its reputation as a democracy with a free press”.

The Jakarta Foreign Correspondents Club issued a statement of concern over Jacobson’s arrest.

“While we of course urge all foreign journalists visiting Indonesia to ensure they follow immigration rules, if a journalist is simply attending meetings or happens to be present during a news event this should not be cause for punitive action or detention,” it said.