The Security Investigation Agency of the Ho Chi Minh City Police Department has issued a third summons for Ngo Thi Oanh Phuong, an influential Facebook user and a critic of conglomerate Vingroup, saying that they received a defamation complaint filed against her by Vingroup, according to a recent Facebook posting of human rights lawyer Dang Dinh Manh.

Previously, Manh wrote on social media that the police had twice summoned Phuong, also known by her Facebook name Phuong Ngo, on Jan. 19 and Jan. 30. In the third summons, dated Feb. 26, they told her to come to the security investigation headquarters on March 4 to question her relations with Tran Mai Son, another critic of Vingroup, and to resolve the defamation report submitted by the conglomerate.

Manh said that Phuong did not come to the previous questioning sessions because she said she was busy. He suggested that if she were absent this time, the investigation agency would issue a warrant to search for her, similar to the warrants the Long An Provincial Police Department filed against him and other human rights lawyers, Nguyen Van Mieng and Dao Kim Lan, last year.

According to Manh, no legal provisions allow Vietnamese investigators to search for people who do not respond to summons. Attorneys Manh, Mieng, and Lan fled to the United States late last year after Long An Provincial Police issued warrants to search for them after they were accused of violating Article 331 of the Penal Code, which concerns “abusing democratic freedoms.”