Maryland Constitution of 1867 Art. 16, § 3

(a) The referendum petition against an Act or part of an Act passed by the General Assembly, shall be sufficient if signed by three percent of the qualified voters of the State of Maryland, calculated upon the whole number of votes cast for Governor at the last preceding Gubernatorial election, of whom not more than half are residents of Baltimore City, or of any one County.  However, any Public Local Law for any one County or the City of Baltimore, shall be referred by the Secretary of State only to the people of the County or City of Baltimore, upon a referendum petition of ten percent of the qualified voters of the County or City of Baltimore, as the case may be, calculated upon the whole number of votes cast respectively for Governor at the last preceding Gubernatorial election.

(b) If more than one-third, but less than the full number of signatures required to complete any referendum petition against any law passed by the General Assembly, be filed with the Secretary of State before the first day of June, the time for the law to take effect and for filing the remainder of signatures to complete the petition shall be extended to the thirtieth day of the same month, with like effect.

If an Act is passed less than 45 days prior to June 1, it may not become effective sooner than 31 days after its passage.  To bring this Act to referendum, the first one-third of the required number of signatures to a petition shall be submitted within 30 days after its passage.  If the first one-third of the required number of signatures is submitted to the Secretary of State within 30 days after its passage, the time for the Act to take effect and for filing the remainder of the signatures to complete the petition shall be extended for an additional 30 days.

(c) In this Article, “pass” or “passed” means any final action upon any Act or part of an Act by both Houses of the General Assembly; and “enact” or “enacted” means approval of an Act or part of an Act by the Governor.

(d) Signatures on a petition for referendum on an Act or part of an Act may be signed at any time after the Act or part of an Act is passed.