Md. Const. art. XVI, § 2

No law enacted by the General Assembly shall take effect until the first day of June next after the session at which it may be passed, unless it contains a Section declaring such law an emergency law and necessary for the immediate preservation of the public health or safety and is passed upon a yea and nay vote supported by three–fifths of all the members elected to each of the two Houses of the General Assembly. The effective date of a law other than an emergency law may be extended as provided in Section 3(b) hereof. If before said first day of June there shall have been filed with the Secretary of the State a petition to refer to a vote of the people any law or part of a law capable of referendum, as in this Article provided, the same shall be referred by the Secretary of State to such vote, and shall not become a law or take effect until thirty days after its approval by a majority of the electors voting thereon at the next ensuing election held throughout the State for Members of the House of Representatives of the United States. An emergency law shall remain in force notwithstanding such petition, but shall stand repealed thirty days after having been rejected by a majority of the qualified electors voting thereon. No measure changing the salary of any officer, or granting any franchise or special privilege, or creating any vested right or interest, shall be enacted as an emergency law. No law making any appropriation for maintaining the State Government, or for maintaining or aiding any public institution, not exceeding the next previous appropriation for the same purpose, shall be subject to rejection or repeal under this Section. The increase in any such appropriation for maintaining or aiding any public institution shall only take effect as in the case of other laws, and such increase or any part thereof specified in the petition, may be referred to a vote of the people upon petition.