Short-seller Carson Block made his name by foretelling the implosion of Chinese-Canadian firm Sino-Forest Corp. Now he and his firm, Muddy Waters Research, have moved on to a bigger target – giant Singapore-based commodities trader Olam International Ltd.

The company, which counts Singapore sovereign wealth fund Temasek among its largest investors, is fighting back by suing Mr. Block for defamation after he called into question the company’s accounting. It’s too early to declare who the victor will be, but the lawsuit underlines the occupational hazards facing anyone who expresses a strongly negative opinion of a company.