Microsoft’s hostile-takeover attempt against Yahoo may encounter an unexpected hurdle in August after a Chinese antimonopoly law takes effect that will extend the nation’s economic influence far beyond its borders.

The law, which goes into effect on Aug. 1, is intended to strengthen an existing set of antitrust regulations the Chinese originally established in 1993. It will make China a third sphere of regulatory influence, matching the power of the European Union and the United States, according to legal specialists in this country and in China who have studied it.

Formally enacted by the National People’s Congress last year, the measure gives Chinese regulators authority to examine foreign mergers when they involve acquisitions of Chinese companies or foreign businesses investing in Chinese companies’ operations. Beijing could also consider national security issues.

The law could give China influence in Microsoft’s courtship of Yahoo because in August 2005, Yahoo, a premier search portal, invested $1 billion in Alibaba.com, China’s largest e-commerce business. The investment gave Yahoo about a 40 percent stake in the Chinese company. Alibaba officials have said they believe that a Microsoft takeover of Yahoo would set in motion a buyback provision, making it possible for them to gain independence from Microsoft.

Nathan Bush, an antitrust law specialist with O’Melveny & Myers in Beijing, said the law represented the ascendance of China “as another regulatory capital contending for influence with Brussels and Washington.”

Inevitable.