Sec. 251.26. Certification; life of; exceptions

When a representative has been certified by the board, such certification shall remain in effect for one year from the date thereof, and thereafter until such time as it shall be made to appear to the board that the certified representative does not represent a majority of the employees within an appropriate unit. In any case where unusual or extraordinary circumstances require such action, or where probable cause is shown that such action may be necessary to prevent the occurrence or continuation of an unfair labor practice, the board, in its discretion, may shorten or extend the life of the original certification. When the board shall find that during the life of a certification the employer has refused to bargain collectively with the certified representative, the time of the continuance of such refusal to bargain shall not be a part of the time limited in computing the life of the certification.