Although officially opening on Tuesday, the rail tunnel will not be fully operational.
"The part that is in service is very limited. All that has been delayed to much later," said Tayfun Kahraman, president of the Istanbul Chamber of Urban Planners. "We are wondering why this inauguration is happening so soon."
Japan's Prime Minister Shinzo Abe will be present at the official opening, as the Bank of Japan was the main funder contributing 735 million euros ($1 billion) to a project that has cost an estimated three billion euros.
Construction of the tunnel that runs 1.4 kilometers (0.8 miles) under the Bosphorus Strait had been scheduled to take four years but was delayed after a series of major archaeological discoveries.
Some 40,000 objects were excavated from the site, notably a cemetery of some 30 Byzantine ships, which is the largest known medieval fleet.
But these unexpected finds eventually frustrated Erdogan, who complained two years ago that artifacts were trumping his plans to transform Istanbul's cityscape.