The American Family Association, a powerful Christian group, has emerged as a key player pressuring Heinz to pull its Deli Mayo commercial featuring two men kissing – even though it was never broadcast on US TV.

Heinz's US HQ was flooded with emails complaining about the Deli Mayo ad, which was only broadcast in the UK, after the AFA found out about it via the internet and mobilised its 3.5 million members.

The AFA, which says it stands for "traditional family values" and targets the "influence of television and other media" on society, sent an email "action alert" to its 3.5 million subscribers denouncing the Heinz Deli Mayo commercial as the "kind of ad we can expect to see in California as they prepare to vote on homosexual marriage".

"I thought you might be interested in seeing the Heinz ad featuring a homosexual family and two homosexuals kissing," said the email action alert.

"We suggest you forward this to all your family and friends letting them know of the push for homosexual marriage by Heinz. This ad is currently running in England, but no doubt can be expected in the US soon."

The action alert, sent out on June 24, included the phone numbers of Heinz's US corporate headquarters and an email letter of complaint for subscribers to support.

Cindy Roberts, the director of media and public relations at the AFA, told MediaGuardian.co.uk that after the alert was sent out Heinz US called to let the organisation know the ad would not run again.

Roberts said Heinz had admitted that the volume of AFA members' email complaints had "bogged the [computer] system down".

The AFA alert was sent out a day after MediaGuardian.co.uk revealed that about 200 viewers had complained about the ad to UK's Advertising Standards Authority.

Heinz UK said it actually pulled the ad on Friday June 20, several days before the AFA got involved.

But Heinz UK only put out an official statement on Monday last week, June 23, saying it had taken the decision to pull the campaign because "some consumers raised concerns over the content of the ad".

A Heinz UK spokesman said the company took the decision after receiving "30 to 40" complaints "from all sides of the debate, not from one side exclusively".

Despite the UK's pre-emptive move, the AFA appears to have applied significant pressure in the US that contributed to Heinz putting out a second, much more strongly worded statement distancing the company from the Deli Mayo TV ad.

"Heinz apologises for its misplaced attempt at humour and we accept that this ad was not in accordance with our longstanding corporate policy of respecting everyone's rights and values," said the statement, which was put out by Heinz US the day after the AFA galvanised its members to protest.

Michael Mullen, the director of global corporate affairs at Heinz, declined to reveal how many complaints - or how many votes of support - the company had received about the TV ad.

"The ad was intended to be humorous and was not intended to be an advocacy ad," said Mullen in an email statement to MediaGuardian.co.uk.

"Heinz made the proactive decision to withdraw the ad before we were contacted by the American Family Association."

Wayne Besen, an executive director of gay advocacy group The Truth Wins Out, appeared on a CNN debate in the US last week discussing the Heinz ad.

In the debate he raised issue of how the AFA, a powerful American lobby group, had played a role in the strong stance Heinz US had adopted over the ad.

"They are a very powerful constituency, a very powerful lobby group. They are one of the top groups in the religious right in America," Besen told MediaGuardian.co.uk.

He added that the AFA had gone after companies including Disney and Ford in the past.

"They have a lot of experience mobilising campaigns and boycotts. They are like a puritanical national nanny," Besen said.

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