Complex sentence: An equally contentious issue was whether to or not to continue with the policy of abstentionism, that is, the refusal of elected representatives to take their seats in parliament; a majority of the leadership was in favour of abandoning this policy.
Split into simpler sentences: An equally contentious issue was whether to or not to continue with the policy of abstentionism, that is, the refusal of elected representatives to take their seats in parliament. A majority of the leadership was in favour of abandoning this policy.