The Spanish parliament has given the government permission to begin peace talks with Eta if the Basque separatist group lays down its arms.
Spain's prime minister said Eta's "destiny" was to lay down arms
The ruling Socialists' motion was backed by six minor parliamentary groups, but fiercely opposed by the conservative Popular Party (PP).
For decades Eta has waged a violent campaign for an independent homeland in northern Spain and south-west France.
Previous Spanish governments have held unsuccessful secret talks with Eta.
A rival motion from the PP on Tuesday called for the Communist Party of the Basque Country (Ehak) to be banned.
It said Ehak was a front for Eta's outlawed political wing Batasuna.
Newly-formed Ehak won nine seats in last month's elections to the 75-seat Basque regional parliament, possibly with votes from previously Batasuna supporters.
Basque police said Eta was responsible for four small bombs that exploded on Sunday at industrial sites in Spain's Basque region, injuring three people.
The blasts came four days after Spanish Prime Minister Jose Luis Rodriguez Zapatero urged Eta to disband in his state of the nation address.
A Socialist administration conducted negotiations with Eta in 1989 and the PP under Jose Maria Aznar did so in 1999.