Another well-known blogger has been arrested, as the authorities continue their campaign to silence independent voices.
Ho Van Hai was detained in Ho Chi Minh City and accused of distributing anti-state information on the internet.
The 52-year-old blogger is being held in isolation and investigated on a charge of spreading propaganda against the state under Article 88 of the penal code, which is often used against political activists and human rights campaigners.
The police gave no details of the charges against him.
Hai’s blog and Facebook page are no longer accessible.
He has posted articles on social media about suspected government corruption, and has called for government accountability over the environmental disaster that blighted the north-central coast after a toxic leak from the Formosa steel plant in April.
The Communist authorities appear acutely sensitive to criticism of their handling of the leak and the mass poisoning of fish that affected the livelihoods of tens of thousands.
Fishermen and their families in the worst affected provinces have joined a protest campaign, with thousands submitting lawsuits to demand more compensation.
Last month, the human rights blogger, Nguyen Ngoc Nhu Quynh, who wrote under the name of Me Nam (Mother Mushroom), was arrested and also charged with spreading propaganda against the state under article 88 of the penal code.
She had taken on a leading role in the campaign for transparency over the Formosa leak.
She has been held in isolation since her arrest on October 10.
The Communist authorities resumed political trials against prominent government critics this year. Independent bloggers say the political mood is deeply oppressive, with their activities and movements closely monitored by the security services.