Article 265, paragraph one of the 2007 Constitution prohibits MPs and senators from holding positions in government agencies, state offices, state enterprises, local assemblies, local administrative offices and the local civil service.
Chusak said the legal interpretation was vital because the six coalition parties had already prepared to nominate MPs to assist in the work of Cabinet members.
Council secretary general Khun Pornthip Jala said she should be able to clarify the ban by the next Cabinet meeting on Tuesday.
Prime Minister Samak Sundaravej said he would abide by the council's interpretation while awaiting a judicial review.
If the council ruled against appointing MPs to executive offices, one of the coalition parties might initiate a test case by nominating one partylist MP as a ministerial secretary or adviser in order to ask the Constitution Court to rule on the issue, he said.