Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
Zulu's suspension took effect from Monday while an internal investigation is already under way.
Zulu was suspended after allegations of misconduct were levelled at him.
Gaal spokeswoman Shonisani Lukoto confirmed yesterday that Zulu had been placed on precautionary suspension "while the authority investigates allegations of misconduct against him".
Zulu's suspension, Lukoto said, was with full pay.
She said if the allegations were proven to be true the board would "most likely take appropriate disciplinary action".
Lukoto did not want to be drawn into discussing the circumstances that led to Zulu's suspension.