Workers at Israel's three main airlines went on strike on Sunday, stopping their outbound flights in protest at the government's plans to ratify an open skies deal with Europe they see as a threat to their jobs.

Supporters of the open skies deal say its relaxation of restrictions and quotas on flights between Israel and European Union countries would increase competition, lower prices and boost Israel's tourism industry.

But Ofer Eini, the head of Israel's Histadrut labor union, said the agreement could leave Israel's airlines struggling to compete with their European counterparts and cost about 17,000 jobs.

"The way in which (this deal) is being implemented will on the one hand bring a reduction in airfares but it will also cause Israeli companies to collapse," he told Israel Radio.

Workers at El Al , Arkia and Israir started their open-ended strike at 5 a.m. (0200 GMT) but the carriers brought forward most departures so that outgoing passengers could leave Israel. Flights coming into Israel and foreign airlines were not affected.

Eini called on the cabinet, which was expected to ratify the agreement later on Sunday, to delay its vote by a month to allow further discussion on adapting the plan to ensure the airlines could continue to compete.

"We are asking for a delay of a month to ensure that (the airlines will not collapse), nothing will happen if we wait another month" he added.

Transport Minister Yisrael Katz said the cabinet would approve the agreement and that it could not be changed because its European signatories had already signed it. He urged the unions to call off the strike.

"The government will ratify the deal today ... the open skies agreement is the only way for El Al to economize at long last and to change its approach so that it can compete in the tough world market," he told Israel Radio.

Katz, a member of Prime Minister Benjamin Netanyahu's right-wing Likud party, has said the deal contained risks as well as benefits and airlines should "exploit the opportunity to compete more vigorously with European airlines".

(Writing by Ori Lewis; Editing by Andrew Heavens)