Fire Emblem: The Age of Legend
A council of peers acting as part of the government of Yeoria. The Akt dates back to the beginnings of the country around 2A 3049 when King Dinmerfin of Yeoria on his path to rulership needed the help of many former petty princes and did not have the strength to totally crush the others. Instead, he garnered the support of many of his former enemies by allowing them to stay on as part of this council with a voice in overall government as well as great autonomy and authority in their own lands.
Generally the monarchy of the House of Yeor can make whatever decisions they need to with regards to taxation, compulsory contributions to the militias, building roads and public works, managing national defenses and whatnot. The king is also directly in charge of his own lands of course. However, the formal approval of the Akt is needed to secure the succession, to approve any uneven tax changes, to approve national actions against any member duchy, and to formally declare war (without which even the king may not command the armies into foreign lands or otherwise make a hostile move.
During the beginning of the Yeorian Succession Crisis of 2A 3214, a faction of secretly rebellious dukes under Duke Grenfeld tied up the normal proceedings that would have approved Prince Rinvolin of Yeoria for the throne while they and their allies in the Northern Principalities secretly gathered their forces. While they were ousted from the Akt when they officially declared that they supported Duke Grenfeld for the next king and the northerners invaded, this means Prince Rinvolin still has not been approved as king and so still does not have full command of the armies.