US healthcare conglomerate Johnson & Johnson became the latest company to suspend all digital advertising on Google’s You Tube, over concerns that its ads may have appeared on channels that broadcast offensive videos.

Wireless carriers Verizon and AT&T said on Wednesday they would suspend digital ads on You Tube, joining a list of well-known British brands such as retailer Marks and Spencer Group plc deserting Alphabet Inc’s Google.

Google has come under intense scrutiny for ads appearing alongside videos on You Tube carrying homophobic or anti-Semitic messages. The company on Tuesday vowed an overhaul of its practices.

Control over online ad placement has become a hot button for advertisers, with social networks and news aggregators coming under fire during and after the US presidential election for spreading so-called fake news reports.

Advertisers have also sought to avoid having their brands appear beside content that they categorise as hate speech.

J&J said yesterday it wanted to ensure that its product advertising did not appear on channels that promote “offensive content.”

You Tube has been a key driver of growth for Google as its traditional business of search advertising matures. Google’s net ad revenue worldwide from You Tube was $5.58 billion last year, according to New York-based research firm eMarketer.

You Tube was not immediately available for comment.

As advertisers revolt, the search giant faces both a short-term loss of revenue and a long-term danger that companies will lose faith in the automated placement of ads upon which Google has built its empire, said analyst Jan Dawson of Jackdaw Research.

“The bigger risk is this seems to be a backlash against programmatic advertising in general,” Dawson said. “There’s this worry that you no longer have control over where ads appear.”

AT&T is removing ads from the non-search inventory on Google because its “ads may have appeared alongside You Tube content promoting terrorism and hate,” the company wrote in an e-mail. Verizon said it had suspended all digital advertising not related to search after saying earlier on Wednesday that it had only suspended advertising on Google’s non-search platforms. It took the action after its ads were appearing on “non-sanctioned websites,” a spokeswoman wrote in an email.

“We are working with all of our digital advertising partners to understand the weak links so we can prevent this from happening in the future,” the spokeswoman said.

Google declined to comment on individual customers but said it has begun a review of its advertising policies.

One question many people are asking is whether advertisers will reallocate the marketing dollars they have devoted to You Tube to other platforms, said Brian Wieser, an analyst at Pivotal Research. Wieser, however, thinks that if the boycott is widespread enough, no one else will benefit.

“If you know all of your competitors are reducing their spending too, then you don’t need to spend more,” he said.

Google must walk a fine line between giving advertisers more control and alienating the massive community of content creators who have made the site a top destination for coveted young viewers. One likely path forward for Google is to tighten controls on which videos are eligible for advertising, perhaps by the channel’s track record or number of viewers, said Dawson.