Zeid Ra'ad Al Hussein, who has been in Fiji this week, met with civil society leaders, who expressed concerns at the limits placed on dissenting voices.
He said the penalties on both journalists and media organisations in the Media Industry Development (Amendment) Act 2015 inhibit investigative journalism and coverage of issues that are deemed sensitive.
And Al Hussein said this discouraged a plurality of views on issues.
He said there was also talk about regulating hate speech and fake news.
"I have urged the government to ensure that any attempts to legislate on issues relating to freedom of expression are in line with Articles 19 and 20 of the ICCPR [the International Covenant on Civil and Political Rights] and for them to consult the Rabat plan of action for guidance on drawing the delicate lines between permissible speech and speech that may amount to incitement."
He also called Fiji's government to ratify two key human rights covenants.
Mr Al Hussein praised the leadership shown by Fiji on climate change, but said human rights is inextricably linked to climate change issues.
He said he had urged the government to ratify the International Covenant on Civil and Political Rights and the International Covenant on Economic, Social and Cultural Rights as the world marks the 70th anniversary of the Universal Declaration of Human Rights.
"I urge Fiji to accede to both covenants and to ensure that its legislation is in line with their provisions. I welcome the government's commitment to ratify all nine core international human rights treaties by 2020.
"I also call on the government to withdraw its reservations to the UN Convention Against Torture, particularly regarding the definition of torture and access to remedies, and ratify the option of protocol to this convention."