The ministers, all members of President Recip Tayyip Erdogan's ruling Justice and Development Party (AKP), were allegedly involved in money laundering, bribery and fraud.
Earlier this month, an investigative commission voted not to send the potentially incriminating files on the four ex-ministers, obtained during the probes last year, to the legislative body.
The allegations broke in December 2013, when the Prosecutor's Office carried out two corruption probes. Investigators alleged that Turkish officials had been buying oil from Iran, despite UN sanctions. The second probe named members of Erdogan's family, at which point he declared the probe a "coup attempt" by followers of rival Islamic opinion leader Fetullah Gulen.  Reuters reports that, in the aftermath of the investigation, thousands of police officers and hundreds of judges and prosecutors believed to be Gulen followers were reassigned, while many state officials were dismissed.
The vote blocks the possibility of an independent judicial investigation into the corruption charges against the former ministers. Had their immunity been lifted, they could have been summoned before the Supreme Court.
Transparency International Turkey issued a press release claiming the vote has "taken the culture of political impunity to a dangerous new level." On Transparency International's 2014 Corruption Perception Index, Turkey scored 45/100, a fall from its 2013 score of 50/100, the largest drop in TI’s ranking for the year.
