In the context of the input sentence, determine the relationship between 'Syriza' and 'Alexis Tsipras'.
Options: employer, chairperson, original broadcaster, brand

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