WASHINGTON -- Sens. Patty Murray and Maria Cantwell and a dozen other Senate Democrats are asking the Obama administration to produce scientific justification for its decision last week to block girls 16 and younger from buying the emergency contraceptive Plan B over the counter.

In a letter to U. S. Department of Health and Human Services Secretary Kathleen Sebelius Tuesday, the 14 lawmakers said they are seeking"medical and scientific evidence" behind Sebelius's unprecedented decision to overrule the Food and Drug Administration and block younger teenagers from buying the so-called "morning after pill" without a prescription.

Yet as Sebelius herself has noted, science had nothing to do with it.

"The science has confirmed the drug to be safe and effective with appropriate use," Sebelius said in her announcement.

Instead, Sebelius and Obama -- who endorsed her decision -- depicted it as a judgment call about the maturity of girls as young as 11 or 12 to take Plan B without talking with a health-care professional. Women's health advocates, physicians and others have accused the White House of subverting science to avoid a political battle over reproductive rights.

Plan B is a higher-hormone version of many birth control pills. It can be taken up to three days after unprotected sex and will prevent about seven out of eight pregnancies that might have resulted.

"Nearly half of all pregnancies that occur in the United States each year are unintended. Keeping Plan B behind the counter makes it harder for all women to obtain a safe and effective product they may need to prevent an unintended pregnancy," the senators wrote.

Also signing the letter were Sens. Ron Wyden and Jeff Merkley of Oregon; Kirsten Gillibrand of New York; Barbara Boxer of California; Richard Blumenthal of Connecticut; Daniel Akaka of Hawaii; Carl Levin of Michigan; John Kerry of Massachusetts; Tom Harkin of Iowa; Al Franken of Minnesota; Frank Lautenberg of New Jersey; and Bernie Sanders, an Independent from Vermont who caucuses with Democrats.