A US consumer watchdog agency told Internet search engines Tuesday to ensure they differentiate between search results and paid advertising, to steer clear of "deceptive" practices.
The Federal Trade Commission's consumer protection staff sent letters to search engine companies to update guidance from a decade ago.
The FTC said it took the action because "paid search results have become less distinguishable as advertising, and the FTC is urging the search industry to make sure the distinction is clear," a statement by the regulator said.
"Consumers ordinarily expect that natural search results are included and ranked based on relevance to a search query, not based on payment from a third party," the letters state.
The letters noted that failing to "clearly and prominently distinguish advertising from natural search results" could be a deceptive practice.
They said the search companies should use "visual cues, labels, or other techniques to effectively distinguish advertisements, in order to avoid misleading consumers."
The letters were sent to general-purpose search engines AOL, Ask.com, Bing, Blekko, DuckDuckGo, Google, and Yahoo!, as well as 17 of the most heavily trafficked specialized search engines.
According to the research firm eMarketer, US advertisers are expected to spend nearly $19.49 billion on search ads this year, up 12.4 percent from last year. Google took in some $12.79 billion in search ad revenues last year, or 73.8 percent of the total market.
Explore further: Local media have positive slant toward local businesses, Rice University expert finds