"Zafar's only crime was that he objected to the photographing of women defecating in the open. Those being photographed included the victim's wife and 14-year-old daughter," the Jan Swasthya Abhiyan (JSA) said.
It also alleged that "reports suggest a massive cover up of the incident is being attempted and the perpetrators are yet to be apprehended".
On June 16, the municipal employees in Pratpargh town had tried scaring away women by taking their photographs when they were defecating in the open.
In retaliation, the municipality employees kicked, punched and beat him with a stick, which led to his death, according to the FIR lodged by Khan's elder brother Noor Mohammed.
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"The JSA expresses deep shock over the murder of Zafar, a 55-year-old social worker of Pratapgarh in Rajasthan. He was lynched in a frenzy by municipal employees linked to the government's 'Swachh Bharat Abhiyan'," it said in a statement.
Zafar had in the past submitted a memorandum against the "harassment of women" by civic officials, which included bullying and shaming of women, the JSA said.
Days before the killing, the victim himself had petitioned authorities demanding latrines and other sanitary facilities in the colony, the JSA claimed.
The Jan Swasthya Abhiyan was formed in 2001, with the coming together of 18 national networks that had organised activities across the country in 2000, in the lead up to the First Global Peoples Health Assembly, in Dhaka, in December 2000.