Vietnamese authorities arrested an activist on Tuesday on unknown charges after he posted two short messages on his Facebook page that appeared to criticize his former employer, a water purification company.

The first post on Hoang Van Vuong’s page said, “Whoever has party membership should establish clean water companies to sell dirty water but receive payments for clean water. Easy earn!”

The second post said, “Clean water companies provide dirty water. Who is held responsible?”

Vietnam has come down hard in recent years on activists and individuals who make critical comments on Facebook, which is widely used in the Southeast Asian nation, arresting them on vague charges of “abusing the rights of freedom and democracy” or “spreading anti-state propaganda.”

Last year, authorities convicted and imprisoned at least 31 such people, handing out prison terms ranging from one to eight years.

Vuong’s younger brother, Hoang Van Quoc, told Radio Free Asia that on Tuesday, Vuong received a call from his former employer asking him to come to the office to pick up a New Year’s gift. Police at the scene then arrested him.

Then the police went with him to his house, asked that the electricity be cut off and read out a house search warrant. They confiscated a camera, a cell phone and a broken laptop. said Hoang Van Long, his older brother.

After that, they made a record of the house search, made six copies, and had Vuong sign one before taking him away, Long said. The police didn’t tell the family what he was arrested for.

Tuyen said he was surprised by the arrest because Vuong was not an influential political dissident and he did not post messages often on Facebook.

Vuong, 44, began voicing critical viewpoints in 2011 and as a result was detained and beaten by authorities that year and in 2012, Tuyen said.

“He is an ordinary person and does not belong to any organization,” Tuyen said. “He spoke up whenever he saw injustice. He only talked about what he witnessed. He sometimes took part in a demonstration together with me or other groups.”

Thong Nhat district police told RFA that they did not have the authority to respond to inquiries about the arrest and suggested contacting Dong Nai provincial police. But someone there said provincial police had not conducted the arrest, and referred RFA back to district authorities.

Facebooker Hoang Van Vuong, 44, was arrested in Dong Nai Province for allegedly criticizing the water authorities. A relatively unknown but outspoken critic of injustice, Vuong began voicing his opinions in 2011 and was detained briefly in 2012. According to RFA, Vuong was called into his former workplace to pick up a gift whereupon he was promptly detained by waiting public security. It is not known what the charges are against Vuong.