Authorities at a prison in Vietnam's Bien Hoa province are threatening female protesters who seek to appeal the jail sentences they were handed last month for their roles in a rare, large-scale demonstration over two controversial government policies, their lawyer said Tuesday. The women are among a group of 20 protesters who were sentenced from eight months up to one and a half years in prison on July 30 for "disrupting public order" in the June 10 protest in southeast Vietnam's Dong Nai province, which official media in Vietnam said had blocked roads and created traffic jams on major highways in the area. Dang Dinh Manh, the lawyer who represented the 20 defendants in their trial last month at the Bien Hoa City People's Court, told RFA's Vietnamese Service that the women among the group are being ill-treated in prison. "I was told by their families that the female defendants have faced intimidation from the prison's authorities," who warned them that if they want to appeal their verdict they would be subjected to sexually transmitted diseases, he said. "I am very upset, because this is a serious violation of the law." Manh said that he had sent a petition to the provincial police to complain about the threats his clients had received. He said he had also met with prison officials who told him that there was no evidence that the defendants had faced intimidation, but promised to conduct an investigation of the claims. Nguyen Thi Kim Vui, the sister of defendants Nguyen Thi Ngoc Phuong and Nguyen Thi Truc Anh, said that during a visit with her siblings, they "cried to me, saying[the prison guards] told them that," but acknowledged that "I don't know if it's true." Vui said her sisters suggested they "were told not to appeal," but are planning to do so anyway. On June 9 and 10, protests rocked major Vietnamese cities including Hanoi and Saigon, also called Ho Chi Minh City, as demonstrators challenged government plans to grant long-term leases for foreign companies operating in special economic zones (SEZs) and the adoption of a controversial cybersecurity law. The protests prompted clashes with police that saw demonstrators beaten and an unknown number detained. Calls for probe and release Manh's claims came a day after London-based rights group Amnesty International called on authorities in Vietnam to launch an independent probe into the death of a farmer who took part in the protests, amid reports that he was tortured in police custody. A local rights group has said that Hua Hoang Anh, a 35-year-old farmer from Kien Giang province died after four police officers visited his home in Chau Thanh district on Aug. 2 to question him about his involvement in the protests, citing his wife who claims she returned from making them tea to find him "collapsed with some injuries to his neck and belly." While the group suggested that Anh may have died of hemorrhaging, police in Ken Giang have said the farmer committed suicide. Local authorities reportedly forced Anh's family to bury him the following day. The claims of intimidation in prison also follow a declaration signed over the weekend by five local civil society organizations and some 50 individuals calling on the government to immediately release the dozens of people detained and convicted in recent weeks for their part in the protests. According to the Aug. 4 declaration, a copy of which was recently obtained by RFA, 52 people have been taken into custody by the police since the protests, including the 20 people convicted in Bien Hoa. "We demand the government of Vietnam to immediately release all people who joined the peaceful protest against the SEZ and cybersecurity laws on June 10," the document reads. "Bien Hoa City should release all 20 people who were convicted in the July 30 trial and annul their sentences, return all property belonging to protesters which was confiscated by the police or court, apologize to the protesters, and compensate protesters who have been illegally detained," it said. The declaration also called on Vietnam's National Assembly, a rubber-stamp parliament, to ensure that legal protections for demonstrators are upheld, according to stipulations in the country's constitution. Rights group Amnesty International estimates that at least 97 prisoners of conscience are currently held in Vietnam's prisons, where many are subjected to torture or other ill-treatment.