NEW YORK (Reuters) - Cristiano Guerra, who has been instrumental in determining the outcome of some of the America's most hotly contested board battles as head of special situations research at Institutional Shareholder Services, is leaving the proxy advisory firm, sources familiar with the move told Reuters.

Guerra will join Strategic Governance Advisors, a unit of strategic advisory and communications consultancy FGS, and reunite with Chris Cernich who had the job at ISS before Guerra, the people said.

Axios first reported the move.