China's tough competition policy is souring the mood for foreign investment, a European business lobby said on Tuesday, in the latest report to criticize Chinese regulators over a series of contentious investigations into international firms. Since August, four foreign business lobbies have expressed alarm about China's antitrust enforcement, an issue many had long been hesitant to address directly. The Washington-based U.S. Chamber of Commerce said on Monday China's actions could be in breach of World Trade Organization rules. Foreign complaints range from worries that foreign firms are being unfairly targeted to concerns over the use of strong-arm tactics by Chinese regulators. "The problem with the recent cases is that they are so in-transparent that it leaves a lot of speculation about the possible intention," Joerg Wuttke, the president of the European Union Chamber of Commerce in China, said. "We have yet to see if it (recent anti-monopoly cases) has an impact on business investment but certainly the mood sours," Wuttke told reporters at a briefing for the launch of the group's annual position paper. The EU Chamber was one of the first foreign lobbies to publicly question the motives behind China's investigations in a statement this August. Other business lobbies, including the U.S.-China Business Council and the American Chamber of Commerce in China, have in recent weeks issued statements and reports citing concerns over China's antitrust regime.