A rally organised by the soldiers' union, the SA National Defence Union, for Saturday in Pretoria has been postponed.

"The postponement came after the Tshwane metro police and the SAPS raised security concerns in relation to the planning and holding of the rally," the City of Tshwane said in a statement.

The rally was supposed to have been held at the Tshwane Events Centre. Though this was considered a private venue there were security concerns, said spokesman Console Tleane.

He said metro police and SA Police Service held a meeting on Friday with Sandu to raise the concerns.

"The major concern with the rally was that there was no clarity with regard to the number of people who were going to attend the rally."

Sandu could not provide clarity on the number and that posed a concern for the police as they needed to know how much capacity they needed to deploy for the rally, Tleane said.

He said there was also no clarity but instead confusion with regards to the actual intention of the rally.

The meeting agreed that a new arrangement would be made for the rally.

"The union will make an application for another rally and the necessary details will be made available in that application so that the police and related services can be prepared for the meeting."

A specific date for the rally was not agreed upon, it would be determined by when the application was made and related logistical considerations, Tleane said.