Md. Code, Tax - General § 10–810

(a) A corporation that, during a taxable year, has Maryland taxable income shall file an income tax return.

(b) Notwithstanding the provisions of subsection (a) of this section, a corporation which is not otherwise required to file a return shall file a return if the corporation:

(1) is not tax exempt under § 10-104 of this title;

(2) is required to file a federal income tax return;

(3) carries on business within this State; and

(4) has income or losses attributable to sources within this State.