Plenary sessions are meetings of all the members of the House. The will of the House is determined at these sessions. The deliberations of each House are, as a rule, open to the public, and business cannot be transacted in either House unless one-third or more of the total House membership is present. All matters are decided by a majority of those present, except as elsewhere provided.
There are four ways of voting at plenary sessions at the House of Councillors: oral (Members are asked whether they have any objections), standing (Members are requested to rise if they are in favor of a question), open-ballot (Members in favor of the bill cast white ballot slips with their names on them and Members in opposition cast blue slips), and push-button (Members cast their vote by pushing the"approval" or "objection" button at their seats). Push-button ballot was introduced into the House of Councillors in January 1998.
Generally, plenary sessions begin at 10:00 a.m. on Monday, Wednesday, and Friday at the House of Councillors and at 1:00 p.m. on Tuesday, Thursday, and Friday at the House of Representatives, when the Diet is in session. During a session, the President has the power to call a plenary session on any other day when he/she deems it necessary.