In his party's parliamentary group meeting on Tuesday, Kemal Kilicdaroglu rejected claims in public opinion that say the CHP would consider a rejection of constitutional changes as a repudiation of Turkish President Recep Tayyip Erdogan.
"When a president comes to power with the nation's votes, his legitimacy will never be discussed," stressed Kilicdaroglu.
The CHP, along with the Peoples’ Democratic Party (HDP), is opposed to proposed constitutional changes that aim to hand wide-ranging executive powers to the president.
Kilicdaroglu said the president's role was to represent 80 million Turkish citizens and to remain impartial.
"If the president is partial, politics will enter mosques, military posts, schools and courts," he said. "If the president is partial, a party leader will appoint a judge. If a party leader appoints a judge, justice dies."
Constitutional reform and the change to a presidential system has been on the political agenda since Erdogan, a former prime minister and Justice and Development (AK) Party leader, was elected president in August 2014.
This marked the first time a Turkish president had been directly chosen by popular vote.
On Jan. 20, Turkish lawmakers from the ruling AK Party and the opposition Nationalist Movement Party (MHP) voted in favor of a new constitutional reform package.
Aside from the change to an executive presidency, other reforms include allowing the president to maintain party political affiliation.
There will be changes to Turkey’s highest judicial body, which would be renamed while retaining its independence and own budget.
The referendum is scheduled to be held on April 16.