To the consternation of marketers and the delight of consumer groups, government officials in China are cracking down on advertising claims.

For years, multinational advertisers had a fairly free hand in China, where regulatory oversight has been less stringent than in developed markets. But recent government actions against consumer-products giant Procter & Gamble Co. indicate a stricter approach.

Television commercials and packaging for four of the Cincinnati-based company's household products, including Pantene shampoo, were banned or placed under investigation last month by authorities in Zhejiang province and Beijing municipality after the company failed to cite the source of its claims -- that Pantene makes hair 10 times stronger, for instance.

P&G stands behind the claims, as do its advertisers, including WPP Group's Grey Worldwide in China, the ad agency that produced the Pantene commercial. "Everything we put on the air is researched and it's true," says Daisy Ching, P&G's brand manager at Grey.

Wang Gang, a Zhejiang official, says an investigation continues and may include a visit to P&G's offices in Guangzhou.

Consumers -- and the groups that zealously protect their interests -- are slowly becoming a force to reckon with in China. In April, P&G paid a $24,000 fine to the Administration of Industry and Commerce in Nanchang after Lu Ping, an insurance agent there, complained that the company's $100 SK-II skin cream wasn't the "miracle water" it claimed to be. Ms. Lu says the product not only failed to make her skin look 12 years younger in 28 days, as its brochures suggested it would, but also caused itchiness and pain.

"I will never believe in any ads anymore," Ms. Lu says.

After a flurry of bad press and inquiries by local officials, P&G withdrew cosmetics-counter brochures carrying the claim. P&G admits the "12 years younger" claim came from the best of its results, and was "an incomplete representation of facts."

The two cases have sent shockwaves through China's booming ad industry as authorities start to vigorously enforce a 1995 law that stipulates statistical claims and quotations "should be true and accurate, with the sources clearly indicated." In April, 11 ministries and committees of the central government joined forces to launch a crackdown on "false and illegal ads," with a focus on cosmetic, beauty, health and pharmaceutical products. Figures from Nielsen Media Research show that such advertising made up about a quarter of all ad spending in China last year.

An official at the State Administration of Industry and Commerce called the crackdown "one of the most important works the State Council will implement this year."

Such ambitious government campaigns in China often go in fits and starts. But in going after a company as large and well-established as P&G, officials are sending a message to the personal-care industry, says Darren Yao, a senior planner at Omnicom Group's TBWA ad agency. "The government punishing P&G can be a very symbolic warning to all the other companies in this industry," he says.

Lydia Price, a professor of marketing at Shanghai's China Europe International Business School, explains the timing by pointing to the expanding role of quasigovernmental consumer associations and aggressive local news media. Wang Qianhu, a director of the China Consumers' Association, says that China will treat foreign and domestic companies alike.

Unaccustomed to such scrutiny in China, advertisers are nevertheless resigned to the change -- the market is too big and promising to quit. P&G, an early entrant after the country opened to foreign business in the 1980s, today counts China as its sixth-largest market. P&G spent $2.5 billion on advertising there last year, according to published rate-card figures, making it the single biggest advertiser in China's $18.9 billion industry, which experts predict will become the world's second-largest, after the U.S., by the end of the decade.

Ad regulation varies widely by country. In the U.S., the Federal Trade Commission has final say over advertising claims, but disputes rarely get to that level. In actual practice, claims are typically scrutinized by competitors and consumer groups, which can then file a complaint with industry's self-regulating body.

In more extreme cases, a competitor can seek a court injunction, such as the one that Energizer Holdings Inc., maker of Schick razors, sought last month against Gillette Co. (which P&G is in the process of buying) for claims that Gillette's M3Power razor could "extend or lengthen hair" and thus slice it more effectively. A federal judge in Connecticut ordered Gillette to remove the claim from its packaging.

A similar system prevails in Japan, while in Europe, most countries combine industry self-regulation with strong government legislation and, in some cases, preclearance of commercials.

But in China, an activist consumer culture is relatively new. "The happenings in the last couple of months have been a good learning experience for us and other multinationals," says Stevie Wong, general manager of P&G's skin-care products in China.

The nuances of navigating China's marketplace have frustrated a number of advertisers besides P&G recently. Just last month, McDonald's Corp. apologized after officials in Xi'an and other cities banned a spot showing a Chinese customer kneeling and begging a store manager for a discount, an image that many Chinese saw as insulting and undignified.

With the P&G controversy, however, the government's concern goes beyond the delivery to contest the claims themselves. "Consumers in China are awake now and want to know the truth, whether it's an international or local brand," says China chief executive Pully Chau of Publicis Groupe's Saatchi & Saatchi.

Internet chat rooms are one example of that vigilance.

"Is it possible that the hair can be 10 times stronger?" read one response to the Pantene ad ban, posted on the People's Daily Web site. "So-called authorized information can be bought by money." Another posting read: "Be alert to those ads which cheat consumers under the banner of 'scientific.' "

Advertisers say they are already cautious about claims they make in China. "Even if we can actually make hair 20 times stronger, we wouldn't make that claim," says Grey's Ms. Ching. "We never push it to the limit. We're very, very careful." But a marketing executive for another multinational brand in China says overstating claims has been standard industry practice.

"Some companies make more aggressive claims in this part of the world," the executive says, adding that companies are now likely to be more careful about what they put in their advertising.

"Before, it tended to be that there was a regulation or a rule that nobody followed, and it was OK to run across the border. And now the government is coming back to stick to that line."