NEW YORK — The renowned breast cancer charity Susan G. Komen for the Cure 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, including all seven in California, and at least one top official has quit, reportedly in protest.

Meanwhile, Komen has been deluged with negative emails and Facebook postings, accusing it of knuckling under to pressure from anti-abortion groups, since The Associated Press reported on Tuesday that it was halting grants that Planned Parenthood affiliates used for breast exams and related services. The grants totaled $680,000 last year.

Planned Parenthood has been heartened by an outpouring of 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 its decision.

“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.