If Jacob Zuma - or any other witness - is not called to test evidence that he was involved in Guptagate, it would be taken as fact, says Sandu.
Not only has Lieutenant Colonel Christine Anderson's evidence implicated President Jacob Zuma, but it is untested, the South African National Defence Union (Sandu) has pointed out.
Sandu previously called for Zuma to be called as a witness to the military tribunal which is investigating military officials, allegedly involved in the Guptagate plane landing at Waterkloof Airforce military base.
Pikkie Greeff, Sandu national secretary, pointed out that Zuma has not been called as a witness; in fact, no witnesses have been called to test Anderson's evidence at all. Thus, the tribunal must accept it, he said.
The tribunal will wrap up its preliminary work on Thursday afternoon.
Greeff said the calls for Zuma to be subpoenaed were partially based on the information contained in Anderson's affidavit, revealed by Beeld on Thursday.
The tribunal can subpoena any witness it deems necessary, empowered by the Military Discipline Supplementary Measures Act, he said, as can the state or the defence.
"The dilemma now is that this is untested evidence. No witnesses were called to refute it. The state will have to consider that in the trial because it will have to try to bring new evidence to refute this, except to call the president?" Greeff said.
He said it was also unclear why none of the teams called Bruce Koloane, the official implicated in Anderson's affidavit as having met and spoken to Zuma about the plane landing.
"If Koloane lied, and did not speak to the president, why continue prosecuting the military personel?" Greeff said.
The presidency on Thursday dismissed allegations that President Jacob Zuma could be implicated in the Guptagate scandal as hearsay.
"While it would not be appropriate to discuss matters that are being addressed at the tribunal, we wish to state categorically that there is no truth to the allegation," said spokesperson Mac Maharaj.
Beeld reported on Thursday that South African National Defence Force members facing a military court on charges relating to the landing of the Gupta plane had implicated Zuma in sworn affidavits.
"On or about April 17 2013, Mr [Bruce] Koloane phoned me and he informed me that he had returned from the president and that the president wanted to know 'if everything is still on track for the flight'," read an excerpt of the affidavit by Lieutenant Colonel Christine Anderson.
"I informed him [Koloane] that we were awaiting the overflight clearance and once this was received, we would be able to finalise the movements of the passengers."
Maharaj said of the allegation: "It is not based on fact, it is based on hearsay".
"This is an old allegation being recycled before a military tribunal that is currently in session."
Anderson (59) also confirmed that Zuma was the "Number One", referred to in a report on Guptagate by the justice department.
"Number One is the president of the Republic of South Africa. For safety reasons we never refer to the president in phone conversations," said Anderson.
She is one of five members of the South African National Defence Force who have been charged before a military court in connection with the landing of a private aircraft at the Waterkloof Air Force Base in April.
Anderson has been suspended from her job for her role in the unlawful landing of the Gupta family's chartered jet at Waterkloof Air Force Base on April 30.
A chartered commercial aircraft, Jet Airways flight JAI 9900 from India, ferrying more than 200 guests for the wedding of Vega Gupta (23) to Aakash Jahajgarhia, landed at the Waterkloof Air Force Base in April.
The passengers were then transported, either by light aircraft, helicopter or in police-escorted vehicles, to attend the lavish ceremony at Sun City's Palace of the Lost City in North West.
The landing sparked widespread criticism and several investigations were launched.
A government investigation exonerated Zuma and his ministers, and found that the landing was the result of "collusion by officials". – Additional reporting by Sapa and Glynnis Underhill