Israeli media has reported that the country's health minister, who heads a powerful ultra-Orthodox political party in Binyamin Netanyahu's coalition, is resigning over railway infrastructure work taking place on the Sabbath, when all labour is prohibited according to Jewish law.
Channel 10 TV and other media reported Friday that Yaakov Litzman told the prime minister he will step down on Sunday over the issue.
It could spell trouble for Netanyahu, who is already under pressure amid an ongoing graft probe, if other Ultra-Orthodox Jewish politicians follow Litzman's lead.
Ultra-Orthodox parties offer Netanyahu support to stabilise his coalition, while the government carves out large budgets for their community's schools and seminaries.
Much of Israel comes to a halt at sundown Friday for the Sabbath.
Israeli police grilled Prime Minister Benyamin Netanyahu for a sixth time on Sunday over allegations of involvement in bribery, fraud, and breach of trust.
Investigators arrived at Netanyahu's official residence in Jerusalem shortly after on Sunday, police said.
Officers of the national fraud and serious crimes squad questioned the premier for "a number of hours" over two cases of corruption.
Netanyahu is suspected of having received luxury gifts from wealthy supporters, including Israeli businessman and Hollywood producer Arnon Milchan.
Netanyahu has consistently denied any wrongdoing and says he has been the target of a campaign by political opponents, openly criticising the media and "left-wing" groups.