Penalizing and imprisoning food safety activists in China has a "chilling effect" on others, says a UN envoy.
Olivier De Schutter, the UN special rapporteur on the right to food, said he had raised the case of Zhao Lianhai, whose child was one of 300,000 made ill in the 2008 scandal that killed at least six infants, with Chinese officials.
Zhao, who was arrested last December after he rallied other victims in the scandal to protest and demand compensation, was sentenced to two and a half years in prison last month. He has reportedly applied for medical parole.
De Schutter, who was wrapping up a nine-day visit to China, said the conviction of individuals alerting the public to food safety risks "creates a chilling effect" on others who would consider reporting violations of the law.
"I think the freedom of expression, and freedom of association such as those that Mr Zhao was exercising are key to protecting social and economic rights such as right to food," De Schutter told reporters.
"Without information flowing freely, without transparency, without the possibility to hold governments accountable, there will be simply less attention paid to the needs of the population and there will be more impunity."
"For this reason, I think a situation such as that of Mr Zhao is a source of concern to all those who defend the right to food," he said.
China's dairy industry was rocked in 2008 by revelations that the industrial chemical melamine was added to powdered milk to make it appear higher in protein, making babies ill and causing worldwide recalls of Chinese products.
Zhao ran a website providing information to families after their babies suffered from melamine-induced kidney stones and urinary tract infections.
A Beijing court convicted him on charges of stirring up public disturbances.
The Chinese Human Rights Defenders, an activist network, this week called on the government to release Zhao, saying his case had been marked "by violations of international human rights standards and Chinese law".
"The Chinese government has convicted him of a crime for his activism, and in the process made a mockery of the legal system and the rule of law," CHRD's international director Renee Xia said in a statement.
China's government insists that citizens enjoy the right to pursue compensation for alleged wrongs in court.
However, people who speak out on sensitive cases are often themselves charged with crimes in what human rights groups say are blatant attempts by the government to silence them.
The milk scandal had worried authorities for its potential to stir social unrest and anger at the government for failing to protect its citizens.