Philadelphia ? The leading organization of U.S. obstetricians and gynecologists Tuesday urged federal regulators to resist conservative political pressure and approve nonprescription sales of so-called morning-after pills.

A Food and Drug Administration advisory panel overwhelmingly recommended in December that Plan B, a brand of emergency contraception, be sold over the counter, and the FDA usually follows such guidance. But amid intense pressure from conservative politicians, the agency asked manufacturer Barr Laboratories for more information about teenagers who have used the pills, and postponed a decision from February to this month.

Four prominent physicians from the 46,000-member American College of Obstetricians and Gynecologists on Tuesday decried the delay.

“Plan B is safe and effective,” said incoming ACOG President Vivian M. Dickerson, of the University of California Irvine. “It has no potential for overdose or addiction. … It is easy to use. … By preventing unintended pregnancy, it also prevents abortion.”

Barr Laboratories spokeswoman Carol Cox said the company had discussed possible compromises with the FDA and expected “some sort of decision” by May 21, the deadline for the FDA to rule.

Emergency contraception, which contains the same hormones as regular birth-control pills, is about 89 percent effective in preventing pregnancy after sex if taken within 72 hours of intercourse. But surveys show many women have difficulty obtaining emergency contraception within 72 hours.