Like preventing the family of Sheikh Ali Salman from entering the courtroom, holding the closed-door sessions are contrary to Bahrain’s laws and constitution, al-Wefaq said in a statement.
“We regard the court as politically-motivated and a ploy. As the board of lawyers has said, the court lacks the competence to study the case” the opposition bloc said.
The statement further added that a number of Sheikh Salman's attorneys have been interrogated. "This is also contrary to the courts' procedures."
The first session of Sheikh Salman’s trial was held on January 28. The AL Khalifa regime has barred the members of al-Wefaq party and some other heads of opposition groups as well as independent journalist from entering the trial sessions of the prominent cleric.
Sheikh Salman was arrested in late December 2014 over alleged anti-regime incitements. Manama accuses him of seeking regime change and collaborating with foreign powers.
His arrest has triggered condemnation inside and outside Bahrain, with leaders, governments and international organizations across the world calling for his immediate release.
Back in April, Amnesty International called on the Bahraini regime to release all political prisoners.
The Western-allied kingdom, which is home to the US Navy's 5th Fleet, has been witnessing almost daily protests against the ruling Al Khalifa dynasty since early 2011, with Manama using heavy-handed measures in an attempt to crush the demonstrations.
Scores of Bahrainis have been killed and hundreds of others injured and arrested in the ongoing crackdown on the peaceful demonstrations.