Johannesburg - Operations at the SA National Roads Agency Limited (Sanral) continued on Monday after its building was the target of a bomb threat over the weekend.
"We hope that this week will go well so that business can continue peacefully. This does not bode well with employees who have to work in order to provide for their families," said Electronic Toll Collection (ETC) spokesperson Nicole Wood.
At least three incidents had been reported at the Sanral building in Midrand.
On Sunday, the building had to be evacuated after a bomb threat was reported.
No bomb was found, said Wood.
The premises was also evacuated on Tuesday and Friday after a suspicious powder, initially thought to be anthrax, was found.
ETC later reported that the substance was harmless.
Wood said work at the centre continued on Sunday with no other incidents reported.
Transport Minister Dipuo Peters on Sunday condemned the threats.
She called on law enforcement authorities to act swiftly in their investigation to identifying those responsible for the threats.
"There are elements in society hell-bent on undermining the peace and security of their fellow citizens. These backward and uncivilised individuals have elected to ignore all platforms made available to them by our constitution to raise whatever concerns they may have," Peters said in a statement.
"We call on law enforcement authorities to do all within their powers to bring the perpetrators of these acts to book." Those affected were receiving the necessary attention and help in dealing with the traumatic experiences of the past week, said Peters.