Turkey's opposition alliance vowed on Monday to cut down the president's powers and expand democratic rights as it unveiled its platform ahead of the May elections.
The six parties united against President Recep Tayyip Erdogan also pledged to agree next month on a joint candidate for the presidency.
The opposition's 2,300-point programme aims to roll back many of the powers Mr Erdogan has amassed during his two-decade rule.
"We will shift to a strengthened parliamentary system," it said, adding it "will put an end to the president's power to issue decrees".
The presidential and parliamentary elections on May 14 — the 73rd anniversary of Turkey's first free elections — are widely seen as the country's most consequential in generations.
Mr Erdogan announced last week that the elections would be brought forward from June.
The leadership race is poised to be tight, with opinion polls projecting no clear favourite.
Mr Erdogan served three terms as prime minister from 2003 and was elected president — then a far less powerful post — when his mandates ran out in 2014.
He has since introduced constitutional changes that allow the president to effectively rule by decree.
The opposition pledged to "urgently" amend the constitution and "put an end to the vague and arbitrary restriction of the freedoms of assembly and demonstration".
Mr Erdogan launched sweeping purges after a failed coup attempt in 2016, with thousands detained on terror-related charges.
His ruling Justice and Development party (AKP) has since clamped down on opposition, particularly from the pro-Kurdish People's Democratic Party (HDP) which has hundreds of lawmakers and supporters behind bars.
Its former leader, Selahattin Demirtas, has been in jail since 2016 on charges of insulting the president, while HDP members have been dismissed from official posts and replaced with pro-AKP figures.
The opposition has also vowed to make Turkey's TRT national broadcaster and Anadolu state news agency abide to "the principles of independence and impartiality".
AFP contributed to this report