Johannesburg - South Africa's five franchises have threatened to boycott the 2013 Super Rugby season if any of the current five teams are excluded from the competition.

According to the Rapport newspaper, the Stormers, Bulls, Lions, Cheetahs and Sharks sent a letter of their demands to the SA Rugby Union (SARU).

This followed SARU's decision at the end of January to include the Southern Kings in Super Rugby in 2013.

SARU's 14 unions unanimously voted in favour of including the Eastern Cape team - consisting of the Eastern Province, Border and South Western Districts - in the 2013 season.

At the time, the national governing body said the other South African teams in the cross-continental competition would be confirmed only after proposals from provinces were considered at a meeting in March.

Rapport reported that SARU president Oregan Hoskins reacted with shock when he got the letter.

He told the newspaper that the five franchises demanded that unless SANZAR (South Africa, New Zealand and Australia Rugby) expanded the competition to 16 teams to accommodate six South African teams they would not participate in next year's competition.

Hoskins said he would send the letter to the other nine unions and it "will be in the hands of all unions to decide which teams will play in the Super Rugby series".

South Africa, however, have a challenge on their hands as the current broadcast deal, which allows for 15 teams in the competition according to the conference system, will be renegotiated only in 2016.

SARU deputy president Mark Alexander said at the end of January that the national rugby body would nevertheless lobby its partners at SANZAR for 16 teams to be introduced into the competition.

"There is a window of opportunity with our partners, we are currently preparing a 16 team schedule so that we can go and debate with them," Alexander said at the time.

If SARU fails to negotiate the inclusion of a sixth team one of the existing franchises would have to drop out of the series.

"We understand if one drops out it is very difficult to come back and compete again the following year, it makes it almost impossible," Alexander said.

SANZAR CEO Greg Peters, however, poured cold water on SARU's ambitions ruling out the possibility of expansion.