* Opposition support needed to pass vote on reforms
* 15 leftists say will not support future policy votes
* Threat to Syriza unity also adds to EU doubts (Recasts, adds letter from Syriza lawmakers, context)
By Costas Pitas
ATHENS, July 11 (Reuters) - Greek Prime Minister Alexis Tsipras faces a struggle to contain a widening split in the ruling Syriza party after leftist rebels said they would not back austerity measures pledged to international lenders in exchange for a new bailout deal.
In a vote in the early hours of Saturday, Tsipras had to reply on opposition lawmakers to secure parliament’s backing to present the proposals to EU negotiators, after 10 government deputies either abstained or voted against and seven were not present.
Fifteen of Syriza’s 149 members of parliament said they would not back the government in future votes when the individual policies, promised by Greece in return for much-needed funding from international lenders, come up for approval.
That poses a challenge for Tsipras as he tries to pass measures that include hiking VAT, cutting defence spending and selling off key state-owned assets, plans which many of his lawmakers deeply oppose.
In a statement written before the vote, 15 lawmakers who belong to the party’s Left Platform said that backing the government in parliament this time did not mean they would vote through individual measures in future.
“(Our support) cannot be taken as a ‘Yes’ to the implementation of austerity measures and neo-liberal demolition, which we will fight against in a movement with workers and the people,” they wrote.
Opposition from within Syriza will also worry euro zone finance ministers who were meeting in Brussels on Saturday to consider the package of reforms, with many deeply sceptical that Athens will fulfil its promises.
“Can the Greek government be trusted to do what they are promising, to actually implement in coming weeks, months and years. I think those are the key issues that will be addressed today,” the head of the Eurogroup of finance ministers Jeroen Dijsselbloem said.
In Athens, Greek Economy Minister George Stathakis said dissenting lawmakers should step aside if they disagree with the government’s proposals, adding that it made sense for some ministers to be replaced.
One of the signatories to Saturday’s letter was Deputy Foreign Minister Nikos Chountis, one of four prominent Syriza figures to have not backed Tsipras.
Parliament speaker Zoe Constantopoulou, Energy Minister Panagiotis Lafazanis and Deputy Labour Minister Dimitris Stratoulis also failed to endorse the government’s plans. (1 US dollar = 0.8960 euro) (Editing by Robin Pomeroy)