Turkey's pro-Kurdish opposition party, the HDP, has vowed to halt all activity in the country's parliament after its joint leaders were arrested.
Selahattin Demirtas and Figen Yuksekdag are accused of spreading propaganda for militants fighting the Turkish state.
They and 10 other activists deny links to the PKK Kurdish rebel group.
President Recep Tayyip Erdogan has hit back at international critics after the arrests, accusing Europe of "abetting terrorism".
Turkish Prime Minister Binali Yildirim said HDP members would be betraying the public if they failed to attend parliament.
The party said its MPs would not resign, but nor would they take part in sittings.
Hours after the HDP members were arrested, a huge car bomb killed eight people and wounded more than 100 in the south-eastern city of Diyarbakir.
Turkish authorities blamed the outlawed PKK (Kurdistan Workers' Party), but the so-called Islamic State group later claimed the attack through its Amaq news agency.
'Europe aids terrorism'
Responding to global criticism over the arrests of the HDP leaders and activists, Mr Erdogan accused Europe of aiding terrorism through its support for the PKK, and said he did not care if Europe called him a dictator.
"Europe, as a whole, is abetting terrorism," he said in a televised speech. "Even though they declared the PKK a terrorist organisation, this is clear... We see how the PKK can act so freely and comfortably in Europe."
"I don't care if they call me dictator or whatever else, it goes in one ear, out the other. What matters is what my people call me," he said.
Mr Erdogan said that parliamentarians behaving as terrorists would be treated as such.
Militants have been fighting for years to achieve independence for the Kurds, who are Turkey's biggest ethnic minority.
But hopes of an end to Turkey's decades-long Kurdish problem have evaporated since a ceasefire with the PKK broke down in 2015, leading to a wave of tit-for-tat attacks.
Turkey remains under a state of emergency that was imposed after a failed military coup in July.