Md. Code Ann., Tax-Gen. § 10-812 — § 10-812

(a) A corporation exempt from income tax under § 10-104 of this title shall file an income tax return if the corporation:
(1) has unrelated business taxable income, as defined under § 512 of the Internal Revenue Code;
(2) is exempt from taxation under § 501(c)(2) of the Internal Revenue Code; or
(3) is an S corporation that is incorporated or does business in the State.
(b) An organization that is exempt from taxation under § 501(c)(3) or (4) of the Internal Revenue Code may file an income tax return to claim a refund under § 10-714 of this title.