Cord leader Raila Odinga has said IEBC commissioners' continued stay in office only delays the reconstitution of the electoral body.
Mr Raila said Isaack Hassan and his team should have vacated office long ago.
He said the corruption allegation leveled against the IEBC officials were enough to compel them leave office.
"Holding public office is primarily based on enjoying public confidence," Raila said through his official Facebook page.
"The moment the public no longer has confidence in the holders of a given office is the moment it behooves the office holders to vacate. This allows institutions to retain and enjoy legitimacy in the view of the public."
Raila flew to South Africa on Thursday to attend a conference on 'The Future of African Cities' and is expected back in the country before Monday when he will lead opposition supporters in yet another demonstration against the IEBC.
The last demonstration held on May 16, was bloody as police clobbered demonstrators along University Way, Nairobi and Kisumu.
The Cord leader said police used live bullets while dispersing demonstrators.
"The People do not exist for the IEBC but rather the IEBC exists for the people and as such must serve the greater good of the people," he said.
"It is time for the commissioners to vacate and pave way for reform of the institution to allow peaceful, free and fair elections in 2017."
IEBC chairman Issack Hassan, however, says he will not resign despite protests by Cord and accused Raila of character assassination.
"We dare Raila to produce any evidence today and we will resign immediately," he said on May 5.
He told Raila to stop the protests and instead engage in dialogue in his quest to disband the IEBC.