The UN Office of the High Commissioner for Human Rights (OHCHR) announced Friday that they are “deeply troubled” by the detention of environmental human rights defender Hoang Thi Minh Hong in Ho Chi Minh City, Vietnam. Hong’s detention is the fith in a series of alleged tax evasion cases that Vietnamese authorities have brought against environmental human rights defenders in the region.

On Wednesday, Vietnamese Police Division for Economic Crimes detained Hong, along with her husband and several others, before issuing a temporary detention order based on tax evasion charges. Nguoi Viet, a Vietnamese-language newspaper published in the US, stated that deputy spokesperson for the Ministry of Foreign Affairs Nguyễn Đức Thắng dodged questions about Hong’s arrest on Thursday. Viet Nam News, a Vietnamese newspaper published by Vietnam’s government, reported Thắng highlighted how the government has “a firm, strong commitment to environmental protection, climate change response, and green and sustainable growth.”

Speaking to Hong’s charges, Human Rights Watch’s (HRW) Phil Robertson said, “Vietnam’s selective use of its vague and flawed tax law to target environmentalists and climate change activists with politically motivated prosecutions is a new, extremely troubling development.” Robertson went on to call Vietnamese authorities’ actions an “arbitrary persecution,” alongside the hashtag “#FreeHoangHong.”

The US also voiced concern over Hong’s arrest on Friday. US State Department spokesperson Matthew Miller called upon Vietnam “to respect the rights of those detained and to respect and protect the freedoms of expression and association for all Vietnamese people.”

The UN OHCHR also noted their concern about the broader issues of arrest, arbitrary detentions and disproportionate sentencing in Vietnam—especially as they relate to journalists, bloggers, Facebook users and social activists. The office warned, there are “serious concerns about the independence of the judiciary, the right to fair trial, standards of treatment in detention, and the severity of sentences imposed on those prosecuted for exercising their fundamental rights, in particular the freedom of expression.”

Ultimately, the UN OHCHR called upon Vietnam’s government to review these laws and ensure they are compliant with international human rights law. They also called for the release of Hong and others similarly arbitrarily detained under Vietnamese law.

Among those similarly detained is Dang Dinh Bach, who was arrested on the same grounds last year, is currently serving a five-year prison sentence. Vietnamese authorities also arrested and sentenced political activist Tran Van Bang to eight years in prison in May for “spreading anti-government propaganda.”

Hong previously closed down her environmental non-governmental organization, known as Change VN, where she served as CEO.