FRANKFURT, June 1 (Reuters) - Thyssenkrupp's chairman on Saturday defended a move to sell a stake in the group's steel unit to Czech billionaire Daniel Kretinsky against the will of worker representatives, adding the company could not afford to delay critical decisions.

Powerful labour leaders at the German conglomerate, who hold half the seats on its supervisory board, are in open conflict with management, arguing they are being sidelined in Thyssenkrupp's efforts to sell its steel business TKSE.

A plan to sell 20% in the business to Kretinsky could only be approved by the board because the vote of chairman Siegfried Russwurm counts twice in the event of a stalemate.

"We've hit rough waters with the steel business. Time plays a major role here. Especially as Thyssenkrupp has been waiting for too long," he told weekly Welt am Sonntag, adding - in a potential warning against strike action - that any suspension of production could damage the business.

"The steel business must no longer be the risk that drags down all other areas of the group. We need a solution, not maybe or at some point, but now."

Russwurm did not rule out using his double vote in future stalemates, adding it was the duty of a chair to ensure appropriate decisions are made.

Germany's biggest union IG Metall earlier this week said that TKSE needed 4 billion euros ($4.3 billion) in funds for a standalone future. Thyssenkrupp wants to create a 50:50 steel joint venture with Kretinsky and pare back funding.

Russwurm said he expected all stakeholders to work together to develop a future strategy to ensure that TKSE, which has come under pressure from high energy costs and cheap Asian imports, can be self-sustainable.

"Otherwise, it is only a matter of time before this company no longer exists."

($1 = 0.9224 euros) (Reporting by Christoph Steitz Editing by Mark Potter)