The Korean Teachers and Education Workers Union (‘KTU’) was notified by the administrative authorities in October 2013 that it could not be regarded as a trade union under the law, which is becoming legal issues about a report and a review system of the registration of trade unions. There are two types in a review system of the registration of trade unions by the administrative authorities under Trade Union and Labor Relations Adjustment Act. One is the prior review system in which a review is carried out in the establishing stage of the trade union. By the system, a certificate of report of registration is issued or is turned down. The other is the ex post facto review system. After an union is issued with a certificate of report of registration, a review is carried out and the administrative authorities can require for correction in the system. The union that fails to perform the requirements would be notified by the administrative authorities that it cannot be regarded as a trade union under the law. The legal basis of this is the article 9 (2) of Enforcement Decree of the Trade Union and Labor Relations Adjustment Act. It states that (2) Where, after a trade union has been delivered a certificate of report of registration, there arise such grounds for returning the written report of registration as falling under Article 12 (3) 1 of the Act, the administrative agencies shall demand correction within the specified period of 30 days, and if the correction is not performed within the period, they shall notify the trade union in question that it shall not be regarded as a trade union provided for under this Act. With an union registration report, when the written report of registration is returned or the trade union in question is notified that it shall not be regarded as a trade union by the prior review system or the ex post facto review system, substantive issues are in regard to workers and in particular, a dismissed person in definition of trade unions that the article 2 of Trade Union and Labor Relations Adjustment Act stipulates. The prior and ex post facto review system in an union registration report and definition of trade unions are inseparably related from each other. They should, therefore, be judged and reviewed in the context of mutual relation.