Eight people were injured when six Sibanye buses were stoned in the Witsand area of Atlantis in the Western Cape on Tuesday morning.
Seven passengers and a driver were treated for minor injuries.
"The attacks are linked to taxi operators in the area as we have been intimidated repeatedly and quite openly and told that we should not operate in the area," said Bronwen Dyke-Beyer, spokesperson for Golden Arrow Bus Services (GABS), which owns Sibanye.
"[The SA Police Service] and law enforcement have been made aware of the threats. This is outright criminality and the authorities must take swift action against the perpetrators," she added.
Pictures from the scene showed shattered windows.
Atlantis residents rely on buses for the long journey into the city and back every day for work.
GABS is offering a R200 000 reward for any information which will lead to the arrest and conviction of the perpetrators, including video footage of perpetrators setting buses alight in recent arson attacks in which five buses were destroyed.
Councillor Angus McKenzie of the City of Cape Town's transport portfolio committee "strongly condemned the stonings".
He called on law enforcement agencies to act quickly, saying people who use buses do not do so as a luxury.