The International Freedom of Expression Exchange (IFEX), which campaigns for press freedom, said in a report that Tunisia had censored newspapers, blocked internet sites, imprisoned people for their opinions or media activities and used torture.
"It's like holding an environmental summit in a nuclear power plant," Suhayr Balhassan, vice president of the Tunisian League of Human Rights, said in Geneva on Tuesday following release of the 60-page report on press restrictions in the North African state.
The UN-backed World Summit on the Information Society (WSIS) is planned to take place in Tunisia in November, attended by governments and multilateral groups.
The meeting aims to bridge the so-called digital divide between rich and poor nations and help settle controversial issues such as global control of the Internet.
But IFEX said it feared Tunisia would "use the WSIS to improve its image while continuing to conceal its poor human-rights record".
"Tunisia must greatly improve its implementation of internationally agreed freedom of expression and other human rights standards if it is to hold the World Summit on the Information Society," the group said.
In December 2003, at the first WSIS meeting in Geneva, Tunisia's role as host for the second and final meeting came under fire because of its record on human rights.
"It's like holding an environmental summit in a nuclear power plant"
Tunisian League of Human Rights
IFEX called on Tunisia to end harassment and assaults on human-rights and political activists, including journalist Abd Allah Zuari, now on hunger strike after being deported to a remote village following 11 years in jail.
IFEX also called on the Tunisian government to free Hamadi Jabali, editor of the weekly newspaper Al Fajr, and hundreds held for religious and political beliefs who had never advocated or used violence.
Tunisia is North Africa's most stable and prosperous country, but has been widely criticised for muzzling the press, beating dissidents and restricting political life.
Last year, the country held its second election under a multi-party system since independence from France in 1956. President Zine al-Abidine bin Ali extended his 17 years in power by winning 95% of a vote that opposition parties called a sham.