The ANC Youth League and the SACP in Limpopo protested against the killing of blacks in the province last week.
The outcry came after the case against two farmers accused of kidnapping and murdering a man they allegedly found poaching on their farm was provisionally withdrawn last week.
Richard Mkhari, 47, of Priesca village was found dead last month - two weeks after he vanished. Mkhari was allegedly assaulted and tied up to a tree.
The suspects, Johan van Niekerk, 69, and Gert van Vuuren, 22, were arrested and charged with murder.
But the charges against the two men were provisionally withdrawn pending the outcome of forensic tests.
SACP spokesman, Jack Matlala, said his party was concerned about an increase in the number of people killed on farms.
He said the SACP was concerned about "the way local white farmers did not respect the lives of blacks".
Matlala claimed the worst case was when the son of a farmer and his workers allegedly tortured Allan Rapatsa by squeezing his genitals with a pair of pliers in 2005.
Rapatsa had allegedly been caught stealing copper wire on a farm.
In another incident, a father of four, Nelson Chisale, died after he was brutally beaten, tied to a tree before being thrown into a lions' den in Mokwalo White Lion Project farm near Hoedspruit in 2004.
His murderers, Mark Scott-Crossley and co-accused Simon Mathebula, were sentenced to life and 12 years respectively.
Also in 2004, a 23-year-old man, Jealous Dube, was shot and killed after a farmer, Jewel Grosburg, claimed to have mistaken him for a baboon.
Grosburg was later sentenced to life imprisonment.
Last year Wessel Nel, a Thabazimbi farmer, shot and killed an 11-year old boy after he allegedly mistook him for a dog.
Nel was fined R20000.
Police investigations into the Mkhari killing are continuing.