The advertiser backlash to Google is growing.

AT&T (T), Verizon (VZ), Enterprise and Johnson & Johnson (JNJ) have halted ads on certain Google platforms after major brands learned their promotional posts were appearing alongside extremist content.

"We are deeply concerned that our ads may have appeared alongside YouTube content promoting terrorism and hate," a spokesperson for AT&T said in a statement to CNNTech. "Until Google can ensure this won't happen again, we are removing our ads from Google's non-search platforms." (AT&T has agreed to acquire Time Warner, the parent company of CNN. The deal is pending regulatory approval.)

A spokesperson for Verizon said the company "took immediate action to suspend this type of ad placement" and has "launched an investigation" into the issue.

Laura Bryant, a spokeswoman for Enterprise, said the car rental company has temporarily halted all of its YouTube ads. "There is no doubt there are serious flaws that need to be addressed," she said in a statement.

Johnson & Johnson said in a statement that it has decided to "pause all YouTube digital advertising globally to ensure our product advertising does not appear on channels that promote offensive content."

An investigation published last week by The Times in London revealed that ads from brands like the BBC and L'Oreal were placed near inappropriate content on YouTube posted by religious extremists, a Ku Klux Klan leader and more.

The British Government, Havas, The Guardian and others halted their Google ads after the investigation.

Related: Google boss apologizes after ads shown on extremist videos

Matt Brittin, head of Google's European business, apologized this week to "our partners and advertisers who might have been affected by their ads appearing on controversial content."

Google followed up by announcing plans to boost resources for reviewing content and to make it easier for brands to control where their ads appear.

"We don't comment on individual customers but as announced, we've begun an extensive review of our advertising policies and have made a public commitment to put in place changes that give brands more control over where their ads appear," a spokesperson for Google said Wednesday.

Google's ad sales still account for the overwhelming majority of its overall revenue, even as the company expands into hardware, self-driving cars and life sciences.

"Overall, we think that the problems which have come to light will have global repercussions as UK marketers potentially adapt their UK policies to other markets and as marketers around the world become more aware of the problem," Brian Wieser, an analyst with Pivotal Research Group, wrote in an investor note this week.