Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: brand, chairperson, employer, original broadcaster

The vote, expected in the early hours of Friday, will test the strength of a rebellion by anti-austerity Syriza lawmakers, which could raise pressure on Prime Minister Alexis Tsipras to call snap elections as early as September.
chairperson