Advertising trade groups spent years developing standards for online ad viewability before they were approved earlier this year. Now, one of the world's biggest marketers and a major media-buying company have officially come out and said those standards aren't high enough.

Unilever and GroupM, whose Mindshare agency handles the marketer's buying, are working with standards for online display and video ads tougher than those set through a process started more than two years ago by the cross-industry Making Measurement Make Sense (3MS) group. That initiative included the Association of National Advertisers, of which Unilever is a member; American Association of Advertising Agencies, to which GroupM belongs; the Media Rating Council, which is charged with evaluating measurement systems; and the Interactive Advertising Bureau.

Unilever's higher standards raise questions about whether the industry's online standards will stick and whether broader industry efforts to develop cross-platform media metrics can win universal acceptance.

For display, Unilever's policy is that 100% of an ad must be viewable in a browser, though it doesn't specify a length of time, according to Rob Master, VP-media for the Americas at Unilever. The 3MS standard is at least 50% of an ad must be viewable for at least a second.

For online video, Unilever only counts ads where 100% of the player is in view; a person clicks to start it rather than having it play automatically; at least half the ad plays; and the sound is on. The 3MS standard is only that only 50% of the video be in view for at least two seconds.

Unilever's standard isn't really that stringent, said Ari Bluman, chief digital investment officer of WPP's GroupM. "What we're asking for is that we no longer want to buy ads that are not viewed by human beings."

The 3MS standards are minimalist by design, meant to measure an "opportunity to see" comparable to what other media impressions are built around. The premise is that people who are interested will pay attention longer than a second or two.

In one respect, the 3MS online standards are tougher than those for TV, where ratings used as currency in negotiations are based on average viewership of commercial pods, not individual ads, said Sherrill Mane, senior VP, industry services at the IAB and a key player in developing the 3MS standards. She believes Unilever's video standard, by requiring opt in, also goes beyond what TV ratings count, given that people don't have to click on TV ads to see them.

"Unilever and GroupM are both organizations that actively participated in 3MS," she said. "It's really a shame, because you want to start somewhere and build, not say we did this hard work but I don't care. We're going to take the standard where we want."

Unilever's separate standard could prove "onerous to small- and medium-size publishers," who may feel the need to pay two of the 15 MRC-accredited vendors for measurements to get a full reading of differences in how they count viewership, she said.

"We felt like we need to take a more aggressive position across the board in digital advertising, which is obviously growing a lot," Mr. Master said. Globally, Unilever spends 20% of its media budget on digital, though it doesn't break that down by country.

"We think there's a huge opportunity to bring greater rigor and accountability where so much more money is flowing," he said.

He and Mr. Bluman don't see their standards going against the spirit of 3MS standards, which they say were meant as a minimum, with the ultimate standards up to individual negotiations. Media companies have been overwhelmingly receptive to Unilever's approach, Mr. Bluman said.

Mr. Master believes Unilever will have no trouble finding enough inventory. "People talk about how there are 50 billion ads a day you can bid on, and in total there are 230 million total users in the U.S. So frequency and volume are not issues," he said. "There's an unbelievable amount of inventory, and if it's not viewed by a human, we want it out of the marketplace."

The move comes as the industry works on broader standards for media and return-on-investment measurement under what Association of National Advertisers CEO Bob Liodice in May called a "Measurement Mandate." Part of the plan calls for making TV-style gross rating points the centerpiece of cross-media measurement. But can that happen if advertisers have different standards for what constitutes an online audience?

"I think it will sort out in the end," said Gayle Fuguitt, CEO of the Advertising Research Foundation. "We completely support the work that the MRC is doing in developing a standard. If more people can adhere to that, it's a rising tide that will lift all boats."