110 ILCS 70/36l

Any employee who has successfully passed an original entrance or promotional examination and who has completed his probationary period shall, at his request, be eligible for transfer to any other agency, institution or place of employment in the classification in which he is certified without further examination and without completing another probationary period. Any such transferee shall acquire seniority in the agency, institution or place of employment to which he has transferred only from the date of employment by that employer, but such transferred employee may, on request, preserve his seniority rights in the position from which the transfer was made for the period of one year from the date of transfer.