The crisis for Google over advertisers boycotting YouTube because of ads placed next to hate-speech videos that first set off a storm in the U.K. has now crossed to the U.S.: AT&T on Wednesday said it will not advertise on YouTube until the telco has a guarantee the internet giant has fixed the problem.

“We are deeply concerned that our ads may have appeared alongside YouTube content promoting terrorism and hate,” AT&T said in a statement. “Until Google can ensure this won’t happen again, we are removing our ads from Google’s non-search platforms.”

[UPDATE, 4:10 p.m. ET: Verizon also said it has pulled ads from YouTube and Google’s non-search ad networks over the issue. “We take careful measure to ensure our brand is not impacted negatively,” Verizon said in a statement. “Once we were notified that our ads were appearing on non-sanctioned websites, we took immediate action to suspend this type of ad placement and launched an investigation. 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.” AT&T and Verizon are two of the biggest advertisers in the U.S.]

[According to the Times of London, which initially reported the AT&T move to suspend ads from YouTube, other American advertisers pulling business from YouTube include car-rental company Enterprise and pharmaceutical firm GSK. More than 250 companies and organizations in the U.K. have already suspended ads on YouTube, the paper reported.]

In a statement, a Google rep said: “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. We’re also raising the bar for our ads policies to further safeguard our advertisers’ brands.”

The backlash against ads placed in extremist YouTube videos began last week in the U.K., when it came to light that some ads were appearing against YouTube videos posted by American white nationalists, anti-gay preachers and radical Islamic groups. British advertisers that have said they are pulling ads from YouTube include McDonald’s, the BBC, L’Oréal, Marks & Spencer, HSBC, Royal Bank of Scotland, Lloyds, the Guardian, Audi, Channel 4 and Havas’ British unit.

In response to the chorus of complaints from the U.K. ad community, Google chief business officer Philipp Schindler earlier this week outlined a series of steps the company is taking to allay advertisers’ concerns. “We know advertisers don’t want their ads next to content that doesn’t align with their values,” Schindler wrote in a blog post. “So starting today, we’re taking a tougher stance on hateful, offensive and derogatory content.”

Schindler also said the YouTube team is taking a “hard look” at its guidelines for what content is permitted on the service, beyond what is considered acceptable for ad monetization.

YouTube’s community guidelines already broadly forbid users from posting hate speech, as well as other content like pornography. But how the policy applies to individual videos requires a judgment call. YouTube’s policies define hate speech as content “that promotes or condones violence against individuals or groups based on race or ethnic origin, religion, disability, gender, age, nationality, veteran status, or sexual orientation/gender identity,” or whose primary purpose is “inciting hatred” on the basis of those attributes.