Turkey's opposition parties and rights groups say they plan to send out hundreds of thousands of monitors and volunteers to voting sites across the country during the June 24 presidential and parliamentary elections.
The parties and NGOs on June 21 said that 519,000 volunteers and party-appointed monitors would be deployed to the 180,000 polling stations.
The opposition is looking to end the 16-year-rule of President Recep Tayyip Erdogan despite what they say are concerns about a fair vote.
In April, Erdogan declared that presidential and parliamentary elections would be held on June 24, more than a year earlier than planned, a move that would help him solidify his power.
Turkey is shifting from a parliamentary system to a presidential one in which the president will have more authority. The changes will take effect after the elections.
When he called the election, Erdogan was widely expected to win. But polls have suggested that the presidential vote could head into a second-round runoff on July 8 and that the ruling party may lose its parliamentary majority after 16 years.
Ankara has so far barred at least two European lawmakers from entering the country to act as observers to the election.
The bans affect lawmakers from Germany and Sweden, countries with large ethnic Turkish populations.
Andrej Hunko, a lawmaker for Germany's Left party, had been due to work with the Organization for Security and Cooperation in Europe (OSCE), an intergovernmental body.
"The members of the parliamentary assembly of the OSCE play an important role in observing elections and in strengthening democracy and the rule of law," the OSCE said.