Turkey releases 10 retired navy commanders
The treaty is aimed at demilitarising the Black Sea by setting strict rules on warships' passage through the Bosphorus and Dardanelles straits leading to the Mediterranean.
But Erdogan is planning to build a new canal in Istanbul to the west of the Bosphorus to take the pressure off one of the world's busiest waterways.
Countries such as Russia insist that the new canal must be covered by the old treaty's rules to preserve the delicate balance of power in the region.
Erdogan lashed out at the commanders after convening a special security meeting about the letter.
Turkey's post-Ottoman history is littered with putsches by a military that views itself as the last guarantor of secularism in the mostly Muslim country.
"In a country whose past is filled with coups, (another) attempt by a group of retired admirals can never be accepted," Erdogan said in a nationally televised address.
The Turkish court released the 10 commanders under special supervision that requires them to report to judicial officials at regular periods and bars them from leaving the country.
Four other former admirals were placed under the same controls.
Turkish media had earlier reported that Erdogan's ruling party had also agreed to strip the former admirals of their government-issued apartments.
The 14 former admirals now under judicial control include Cem Gurdeniz -- often described as the father of Turkey's controversial "Blue Homeland" maritime doctrine.
Gurdeniz and some of the others who signed the letter advocate improved relations with Russia and China at the expense of Turkey's position in the NATO defence alliance.