NEW YORK Susan G. Komen for the Cure, the renowned breast-cancer charity, faced an escalating backlash Thursday over its decision to cut breast-screening grants to Planned Parenthood. Some of Komen's local affiliates are openly upset, and at least one top official has quit, reportedly in protest.

Komen has been deluged with negative emails and Facebook postings that accuse it of knuckling under to pressure from anti-abortion groups after reports said it was halting grants to Planned Parenthood affiliates. Planned Parenthood used the grants, which totaled $680,000 last year, to pay for breast exams and related services.

Planned Parenthood has been heartened by support in response to the cutoff. In addition to $400,000 in smaller donations from 6,000 people, it is receiving $250,000 from a family foundation in Dallas and a $250,000 pledge announced Thursday by New York Mayor Michael Bloomberg to match future donations.

In Washington, 26 U.S. senators - all Democrats except for independent Bernie Sanders of Vermont - signed a letter calling on Komen to reconsider.

"It would be tragic if any woman - let alone thousands of women - lost access to these potentially lifesaving screenings because of a politically motivated attack," the senators wrote.

Komen's top leaders, in their first news conference since the controversy erupted, denied Planned Parenthood's assertion that the decision was driven by pressure from anti-abortion groups.

"We don't base our decisions on whether one side or the other will be pleased," said Komen's founder and CEO, Nancy Brinker.

Komen has said the decision stemmed from newly adopted criteria barring grants to organizations under investigation. The new rule affects Planned Parenthood because of an inquiry by a Republican congressman acting with encouragement from anti-abortion activists.

Brinker said Thursday that there were additional factors, notably changes in the types of breast-health service providers it wanted to support. However, she said grants would continue this year to three of the 19 Planned Parenthood affiliates - in Denver, in California's Orange County and in Waco, Texas - because they served clientele with few other breast-screening options.

A source with direct knowledge of decision-making at Komen's headquarters in Dallas gave a different account, saying the grant-making criteria were adopted with the deliberate intention of targeting Planned Parenthood. The criteria's impact on Planned Parenthood, and its status as the focus of government investigations, were highlighted in a memo distributed to Komen affiliates in December.

According to the source, who spoke on condition of anonymity for fear of repercussions, a driving force behind the move was Karen Handel, who was hired by Komen last year as vice president for public policy after losing a campaign for governor in Georgia in which she stressed her anti-abortion views and frequently denounced Planned Parenthood.

Brinker, in an interview with MSNBC, said Handel didn't have a significant role in the policy change.

Among Komen's affiliates, there were clear signs of discomfort with the decision. The Connecticut branch received scores of supportive emails after expressing frustration about the cutoffs and good will toward Planned Parenthood.

The board of the Arkansas affiliate issued a statement noting that the decision was made at Komen headquarters "without input from affiliates," and called for the new policy to be changed.

"We hope Komen national will reverse its position on granting to organizations under investigation because we feel decisions of this nature should be made only after the investigation is complete," the statement said.

At the Orange County affiliate in Costa Mesa, Calif., executive director Lisa Wolter said there have been lots of exchanges with headquarters.

"We're very troubled by the reaction, and we want to make sure there are clarifications," she said.

Though comments posted on Komen's Facebook page seemed to be mostly critical of the grant decision, Brinker said donations to the charity had increased since Tuesday.