A motoring industry engineer convicted of organising protests during the 1989 democracy movement has filed a petition to overturn his 20-year sentence, his father says. Tang Yuanjuan , serving his sentence in Liaoning's Lingyuan Prison, filed his petition in the Supreme People's Court last month asking it to overturn a 1990 guilty verdict by Changchun City Intermediate Court. His father, Tang Jingwu , told a human rights group in Hong Kong his son was seriously ill and urged the authorities to grant him medical parole. He said Tang was suffering from tuberculosis and hepatitis and was required to do hard labour. The Information Centre of Human Rights and Democratic Movement in China claimed that although Tang was only guilty of organising protests, he was given the heavy sentence because police were keen to get credit in cracking down on dissent. Formerly an assistant engineer at Changchun No 1 Motor Works, Tang was jailed for 'organising and leading a counter-revolutionary group' and 'carrying out counter-revolutionary propaganda and incitement'. His father, who visited Tang last week, said he was worried about his son's health. Tang was once included in a prisoner list presented by the United States to China requesting information.