Residents in a number of neighbourhoods in Istanbul, which narrowly voted "no", took to the streets banging pots and pans to protest against Erdogan's victory.
The bar association said a last-minute decision by the YSK to allow unstamped ballots in the referendum was clearly against the law, prevented proper records being kept, and may have impacted the results.
Turkey's biggest cities - Istanbul, Ankara and Izmir - voted "No" on Sunday, along with industrial heartlands, tourist hotspots and ports in 33 provinces, outward-looking regions that have thrived on strong relations with Europe and are increasingly fearful of the future.
However, opposition parties said the exercise was marred by irregularities, adding that they would challenge its result.
Moreover, Anadolu Agency reported that the votes gained 51.4 percent saying President Recap Erdogan need to expand his term while 48.6 percent was unfavorable on the platform.
Some 2,000 protesters in Istanbul Wednesday evening demanded the resignation of the electoral board and chanted "Don't be silent, shout out, "no" to the presidency".
Bulent Tezcan, deputy chairman of the opposition Republican People's Party, or CHP, said the party filed a formal request seeking the referendum's annulment due to voting irregularities. Opposition parties slammed the election commission for accepting unsealed ballots and pointed to conduct irregularities before appealing to cancel the result.
People walk in central Istanbul's Taksim Square, Tuesday, April 18, 2017.
Yildirim said the "the path to seek rights" should be limited to legal objections and urged the opposition to accept the vote's outcome.
However, thousands continued to protest Sunday's referendum, which has set into motion the transformation of Turkey's system of government from a parliamentary to a presidential one that would give more power to President Recep Tayyip Erdogan.
"For years, we have worked on getting ourselves integrated with the world", Serafettin Asut, head of the chamber of commerce and industry in the Mediterranean city of Mersin, home to one of Turkey's largest global ports. "From the German government's point of view, Turkey must. clear up the questions that have been raised".
Erdogan has said the vote on Sunday ended all debate, however, telling European observers who criticised it: "Talk to the hand".
Tana de Zulueta, head of the observer mission of the Organization for Security and Cooperation in Europe, said the ballot decision undermined important safeguards against fraud and contradicted Turkey's own laws.
The White House said they also discussed a USA missile strike in Syria and the fight against the Islamic State group.
His congratulations stands in stark contrast to the more cautious tone adopted by European leaders and a statement issued by the US State Department, which acknowledged the results but warned against further repression by the Turkish government of the political opposition.
The two leaders will meet in May, Turkish Foreign Minister Mevlut Cavusoglu said at a press conference carried by CNN Turk on Wednesday.