Israel's Supreme Court will have to decide whether local rabbis can refuse to marry converts, in what may turn out to be a landmark case.

The latest challenge the rabbis are posing to the converts is an attempt to sabotage the only successful conversion programme still operating in Israel, run by the IDF.

The army's Nativ programme began in 2002 and currently has about 1,000 soldiers a year participating. To convert in Israel through the Orthodox rabbinical courts, a prospective ger must prove to the rabbis that he or she also leads fully mitzvah-observant lifestyle. In the army, this problem has been solved by the fact that the IDF is largely an observant environment, where Shabbat and kashrut are kept by order.

The IDF allows soldiers time off to take part in Judaism classes, which are operated with the Jewish Agency. The conversion itself is performed by the IDF Chaplaincy Corps's beth din.

There are 5,000 soldiers who are not defined as halachically Jewish.

Sarah, an IDF sergeant in the Intelligence Corps who is part of the Nativ programme, says that "for me this is one whole wonderful experience, learning about the meaning of Judaism in the best possible way. I know from friends that the beth din in the army is much more friendly towards people like me than the rabbinical courts outside."

Over the last few years, the number of immigrants trying to convert in the civilian rabbinical courts has dropped due to conversions being revoked by some of the courts and the refusal of many local rabbis to register converts for marriage.

The marriage issue is what is now threatening the effectiveness of the IDF's programme. Its graduates are beginning find out that their conversions are recognised by the state, but are no guarantee that they will be allowed to marry as many marriage registrars - all rabbis - obey ultra-Orthodox leaders who are pushing stricter standards for giyur.

Alina Sardyukov converted in the IDF and has now been refused a marriage certificate by the rabbi of Ashkelon, Yossef Chaim Bloy. Along with her fiancé Maxim and Itim, the Jewish Life Information Centre, which works with converts, she is petitioning the High Court to force four local rabbis who refuse to marry converts to change their policy.

"There is a conflict here because the Rabbinate which is controlled by ultra-Orthodox rabbis is seeing the IDF conversion route as a direct challenge," says Dr Aviad HaCohen, the lawyer who served the petition on Sunday.

"While the government is investing huge resources to promote conversion, it is also financing the courts and local rabbis who are trying to block this. The way they are treating converts conflicts both the democratic and the Jewish ideals which are the state's basis and we hope that the Supreme Court will rule that this is also illegal."