Dissidents from the Nationalist Movement Party launched a campaign to oust Bahceli, 68, after a general election in November in which the party shed half its support - taking just 40 seats in the 550-member parliament compared to 80 five months previously.
Bahceli, who has led the party for 19 years, said in January that the next party congress would take place in 2018, meaning he would be in charge until then.
In a show of unity, MHP's four contenders for leadership, including charismatic former interior minister Meral Aksener, arrived today near the Ankara hotel - the venue of the congress - in the same vehicle, escorted by hundreds of cars.
But they faced iron barricades, with police stationing water cannon nearby and denied entry into the hotel.
Also Read
"Party congresses not party leaders will have the final say," the four candidates said in a joint declaration, near the police barricades.
Party members waving Turkish flags outside the hotel shouted "Bahceli, resign!".
Replacing Bahceli, who lacks appeal with younger voters, could boost support for the MHP at the expense of Erdogan's conservative ruling Justice and Development Party (AKP).
The outcome could jeopardise Erdogan's ambitions of winning a big enough majority in the next elections to allow him to change the constitution to boost his powers.
Four contenders to succeed Bahceli have emerged, including 59-year-old Aksener, a former deputy speaker of parliament seen as the strongest candidate.
They have vowed to press ahead with the congress, despite the legality of the meeting being called into question and police sealing off the venue.
The country's highest appeal court said this week it will rule on the issue within a month, while two lower courts have issued conflicting decisions.
Aksener refused to leave the scene unless she was granted a written official document that they were barred from entry, to use in their legal battle.