Mary Lou McDonald has warned the DUP against any move that could destabilise powersharing in Northern Ireland.
The Sinn Fein president was speaking in Belfast hours before the party election for a new leader following the resignation of Arlene Foster.
Both contenders, Lagan Valley MP Sir Jeffrey Donaldson and Stormont Agriculture Minister Edwin Poots, have vowed to wage war against the Northern Ireland Protocol.
The party’s 28 MLAs and eight MPs will meet virtually on Friday to hear both men’s pitches before voting in a secret ballot.
Mrs Foster confirmed on Wednesday that she would be voting, but declined to say who she would be backing.
Ms McDonald said the leadership of the party is “entirely a matter for themselves”, but she added: “Powersharing has to work for everyone.
“We need to make progress together, we need to be true to and honour the commitments we have entered into in the New Decade, New Approach agreement together and, irrespective of who leads the Democratic Unionist Party, the realities are that we need to implement those agreements, we need to respect and acknowledge the rights of all of our citizens.
“We need to ensure that powersharing, that the Executive and the Assembly is stable and that it works and that collectively we deliver.
“It is very, very unwise in the mouth of a leadership election for anyone in political unionism to be talking about destabilising the institutions.
“The institutions have to work, powersharing has to work, the Good Friday Agreement has to work, Stormont House (Agreement) needs to be delivered, Acht na Gaeilge (Irish language act) and the cultural legislative package needs to be delivered.
“And the reason why all these things need to happen is because that’s how we give each of our citizens the best chance, the best shot at having a decent quality of life and living in a stable, respectful society.”