In an attempt to stem a trend of quasi-condoned premarital sex among young modern Orthodox men and women, Chief Ashkenazi Rabbi Yona Metzger has issued a prohibition against allowing single women to use mikvaot (ritual baths). In a letter dated January 24 and addressed to the rabbis of the Land of Israel, Metzger warns of a trend in which young modern Orthodox men and women use mikvaot to circumvent one of the severest prohibitions connected with sexual intercourse. "It is absolutely prohibited to allow a single woman to immerse herself in a mikve," wrote Metzger. "And it is an obligation to prevent her from doing so." Metzger also advised that ritual bath attendants should be told to prevent single women from immersing themselves. Jewish law proscribes sexual relations with a woman during and after menstruation until she immerses herself in a mikve. This prohibition is known as nidda. Traditionally, only married women have been permitted to remove the prohibition of nidda via a mikve, so they can have sexual relations with their husbands. In contrast, single women have traditionally been prevented from using a mikve because it would, in theory, remove the main prohibition against sexual intercourse. There is no Biblical prohibition against a male and a female having sexual intercourse once the obstacle of nidda has been removed. There is, however, a less stringent rabbinic injunction against premarital sex. In recent years modern Orthodox men and women have been postponing marriage to pursue higher education and careers. Others have simply not found the right person with whom to settle down. As a result, some young Orthodox people, who feel obligated to adhere to Halacha, but who also find celibacy impossibly difficult, have used the mikvaot to remove the main legal obstacle to premarital sex. Prof. Tzvi Zohar of Bar-Ilan University wrote an article in March 2006 condoning premarital sex that aroused fervent debate in religious Zionist circles. Zohar's article, printed in Akdamot, an academic journal on Jewish thought published by Beit Morasha, analyzed the opinions of leading halachic authorities from the Middle Ages, such as Nachmanides, and those of the modern era, such as Rabbi Ya'acov Emden, and showed that many permitted sexual relations without marriage. In an arrangement sanctioned by Jewish law, according to these opinions, the woman becomes a pilegesh, or concubine. Neither the man nor the woman has any obligations or rights, but both must adhere to family purity laws in accordance with Halacha.