Surapong Kongchantuk, chairman of the council's human rights subcommittee, warned defamation laws have been used as a tool to silence those who reveal information that others want to conceal.
Several contentious criminal defamation and Computer Crimes Act cases have been filed against activists, researchers and journalists over the past year.
High-profile cases include the defamation suit against labour rights activist Andy Hall and charges levelled at Phuketwan reporters Alan Morison and Chutima Sidasathian. Both prosecutions concern undercover research or reporting on the plight of migrants in Thailand.
"The more the plaintiffs try to press charges, the more problems they will encounter," said Mr Surapong. "They claim they are doing this to protect themselves, but society does not see it that way. Society sees it as an intimidation."
Mr Surapong urged the new government to drop all cases related to freedom of expression concerning the media and academics. In cases where the plaintiff is a company, the state should persuade the firm to drop charges, he said.
"The government has a duty to ensure freedom of expression is upheld. This is what measures the extent of democracy and peace," he told a forum at the Foreign Correspondents' Club in Bangkok on Monday.
Supinya Klangnarong, a member of the National Broadcasting and Telecommunications Commission, called for defamation to be decriminalised.
"However this will be difficult because we do not currently have a democracy," she said, adding most defamation cases in Thailand aim to save face.