The Coalition of Domestic Election Observers (CODEO) on Friday urged the Electoral Commission to protect the voters' register and other electoral materials in Tuesday's bye-election in Chereponi.
The EC must also guard against multiple voting and voter impersonation by the use of fake voter identity cards, CODEO said in a statement signed by Mr John Larvie, National Coordinator.
It asked security agencies to act professionally and consistently in dealing with acts of intimidation, fraud and violence.
"Any perception of police inaction and bias in the face of palpable breaches of the electoral laws only goes to encourage impunity and insecurity for the people of Chereponi."
CODEO asked executives of political parties to adhere to the letter and spirit of the Public Order Act and other laws regulating political competition, saying it was time for parties to demonstrate good faith and comply with their own internal rules by punishing their supporters who violated the electoral laws and perpetrated violence.
It asked the National Commission for Civic Education, the political parties and other civil society organisations to support the process.