He handed over necessary documents to the National Anti-Corruption Commission (NACC) and said he would be ready to clarify all allegations against him.
He said he jointly signed the proposed charter amendment but was not involved in debate, scrutiny or voting for the bill.
He asked the NACC for 30 days to compile additional documents from related government agencies. The NACC agreed.
Lower House speaker Somsak Kiatsuranont is also scheduled to acknowledge similar charges. The pair were charged by the Democrat Party of breaching the Constitution in their move on the charter review.