Updated

By Ed Stoddard and Ben Klayman

DALLAS/CHICAGO (Reuters) - Women's groups are urging television broadcaster CBS not to air an ad during next month's Super Bowl football championship final because they say it has a strident anti-abortion rights message.

The plans to air the ad, sponsored by a conservative Christian group called Focus on the Family, could see the polarizing issue of abortion rights dropped squarely in the midst of National Football League's premier event.

It would be the first time that Focus on the Family, a politically influential evangelical group founded by James Dobson, has bought air time during the Super Bowl -- the ultimate prize of the advertising world with 30-second spots going for up to $3.2 million.

The Women's Media Center and over 30 other liberal and women's advocacy groups sent a letter to CBS, the TV network to air the Super Bowl on February 7, saying: "... we urge you to immediately cancel this ad and refuse any other advertisement promoting Focus on the Family's agenda."

"We are calling on CBS to stick to their policy of not airing controversial advocacy ads ... and this is clearly a controversial ad," Jehmu Greene, the president of the Women's Media Center, told Reuters.

But CBS said it no longer had a blanket filter on advocacy submissions for ad slots. "We have for some time moderated our approach to advocacy submissions after it became apparent that our stance did not reflect public sentiment or industry norms on the issue," said CBS spokesman Dana McClintock.

An NFL spokesman said: "CBS standards and practices department approved the content of the ad as appropriate for the audience. We take no issue with CBS' decision."

Focus on the Family has said that 30-second spot will feature college football star Tim Tebow and his mother Pam.

"The Tebows said they agreed to appear in the commercial because the issue of life is one they feel very strongly about," it said in a statement on its website.

While the statement does not explicitly mention abortion, "issue of life" is often akin to opposition to abortion rights in conservative Christian circles.

Media reports have said the ad is expected to focus on Pam Tebow's decision to carry Tim to term despite a recommendation from doctors that she have an abortion.

But Focus on the Family spokesman Gary Schneeberger would not reveal the contents, saying: "Tim and Pam are going to share one of their inspirational stories. We will not confirm which one it is because we want the impact of the ad to be felt on Super Bowl Sunday."

Focus on the Family also said the ad had been paid for by "very generous and committed friends" and that no money was used from the ministry's general fund.

"It (the ad) uses one family's story to dictate morality to the American public, and encourages young women to disregard medical advice, putting their lives at risk," said the letter sent to CBS by the Women's Media Center.

Abortion is one of the most divisive issues in America and a spate of recent opinion polls have suggested growing opposition to women's right to terminate pregnancy.

(Editing by Mary Milliken and Chris Wilson)