BEIJING — There’s a tiger fight going on in China.

Regulators on Wednesday issued a scathing report against one of the country’s biggest stars, accusing e-commerce giant Alibaba of failing to do enough to prevent fake goods from being sold on its websites. Uncowed, Alibaba fired back with charges of bias and misconduct by a named Chinese official. Such public defiance is almost unheard of in China.

Even more dubious is the timing of the sternly worded report. The State Administration of Industry and Commerce wrote the report in July after meeting with Alibaba management, but postponed issuing it to avoid affecting the company’s New York stock market listing. Alibaba disclosed the issue of counterfeit goods as a risk factor in its prospectus – but didn’t reveal any investigation by regulators before raising $25 billion in its September IPO.

The controversy dragged Alibaba’s U.S.-traded shares down about 4 percent to $98.45 on Wednesday. It also threatens to cause headaches for Yahoo Inc., which holds a 15 percent stake in the Chinese company. Today’s downturn shaved more than $1 billion from the value of Yahoo’s stake just hours after the California company said it would spin off Alibaba shares later this year.

“If the spinoff was going to occur at the end of this month, there would be nothing to worry about,” says Rosenblatt Securities analyst Martin Pyykkonen. “But if Alibaba’s stock is down by 20 percent six months now, then there could be problems.”

Alibaba’s issues with counterfeit goods are documented. Alibaba.com and Taobao were named in the U.S.’s “notorious markets” report each year from 2008 to 2011, though both marketplaces have since been removed from the list. But Wednesday’s report was the first time China has criticized one of its own, particularly a leading star in an Internet industry that communist leaders are eager to develop.

The report seems to be about “putting Jack Ma in his place,” says Gil Luria of Wedbush Securities.

SAIC has emerged as an aggressive regulator of business in China. It has pursued allegations of corruption and has pressed antitrust investigations against foreign companies including Microsoft and Chrysler. Foreign firms have complained of unfair treatment.