Utilize the input text as a context reference, choose the right relationship between Syriza and Alexis Tsipras from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

But prime minister Alexis Tsipras will have to fight down a rebellion in his Leftist Syriza party, a week after more than 38 of his MPs rejected a raft of tax hikes and pension cuts .

Answer: chairperson