Any person employed by a private employer which employs more than twenty-five persons, or by a municipality in which there is no ordinance or charter provision to the contrary, who leaves such employment to accept a full-time elective municipal or state office shall be granted a personal leave of absence from such employment for not more than two consecutive terms of such office. Upon reapplication for his original position at the expiration of such term or terms of office, such person shall be reinstated to his original position or a similar position with equivalent pay and accumulated seniority, retirement, fringe benefits and other service credits, unless the employer’s circumstances have so changed as to make it impossible or unreasonable to do so. Such person shall give notice in writing to his employer that he is a candidate for a full-time municipal or state office within thirty days after nomination for that office.