"We view the Efrat association's activity, aimed at saving the lives of Israel's children, as extremely important," Rabbis Yona Metzger and Shlomo wrote in an open letter sent to Israel's rabbis.
"In its 30 years of operation, tens of thousands of fetuses have been saved thanks to the association. The lives of some 4,000 fetuses were saved in the past year alone."
Efrat's representatives try to convince Jewish women not to undergo abortions by visiting clinics and offering economic aid to women considering terminating their pregnancy.
The association made headlines recently in a tragic context after the death of an Israeli teenager, Raz Atias, whose young girlfriend was pressured by an Efrat volunteer not to have an abortion.
According to Atias' family, that pressure was what prompted him to kidnap his girlfriend and threaten to commit suicide with her. He was eventually shot to death by police volunteers.
Another row erupted in recent weeks when national-religious newspaper Besehva decided to award the association with a special prize at the Jerusalem Conference being held this week.
A protest is being organized outside the conference under the banner, "Stay out of our womb."
In their letter, the chief rabbis stated that "the wide public must be made aware of the gravity of killing fetuses, which is like actual murder."
The rabbis ordered the Religious Councils' marriage departments to continue handing out the booklet "Ahead of a happy marriage," published by Efrat, due to its "great importance and necessity."
They further wrote that "any rabbi holding a conference on abortion or reproduction issues, or who is active on this matter in any way, should invite Efrat Chairman Eli Shosheim to participate in this activity or consult him as the most senior professional in Israel in this field, as this has proved to really saves lives."