People Power Party lawmakers on Thursday asked the Democratic Party of Korea to apologize after a former aide for one of its lawmakers, Rep. Sul Hoon, came under investigation over suspicion of leaking secrets obtained through the Assembly office.

The former Democratic Party aide, who worked for Sul for nearly three years until March, is being investigated by the National Intelligence Service on suspicion of using the security clearance granted to some Assembly staff to access and leak classified secrets, People Power Party lawmakers said. The suspicion, if true, would amount to a violation of the National Security Act.

The ruling party lawmakers on the National Assembly’s national defense and intelligence committees said in a joint statement that the latest case called for running checks on more Democratic Party aides for other possible instances of abuse of access to classified information.

“The security clearances held by Assembly staff may need to be revalidated in light of the gravity of the recent incident,” they said in the statement. “It is questionable how the former aide was able to pass the background check in the first place, and then work for so long for the Democratic Party lawmaker and leak important information without getting noticed.”

They also called on Sul, a five-time lawmaker, to step down from the Assembly national defense committee.

This is the second time during the current Assembly that an aide or a former aide has come under investigation for violating the law on national security. Previously, a former aide for Rep. Youn Mee-hyang, another Democratic Party lawmaker, resigned following accusations of coming in contact with North Korean authorities while working at the Assembly.