The competition regulator is suing the burger chain in the Federal Court for allegedly making misleading claims about donations to an environmental cause.

The burger chain claimed it was donating $1 per burger sold during the promotion, but the consumer watchdog alleges only 4 per cent of purchases actually qualified.

The burger chain claimed it was donating $1 per burger sold during a promotion, but the consumer watchdog alleges only 4 per cent of purchases actually qualified.