A brief of an amicus curiae may be filed only (1) by leave of the appellate court or a single justice granted on motion or (2) at the request of the appellate court, except that consent or leave shall not be required when the brief is presented by the Commonwealth. The brief may be conditionally filed with the motion for leave. A motion for leave shall identify the interest of the applicant and shall state the reasons why a brief of an amicus curiae is desirable. Any amicus curiae shall file its brief within the time allowed the party whose position as to affirmance or reversal the amicus brief will support unless the appellate court or a single justice for cause shown shall grant leave for later filing, and shall specify within what period an opposing party may answer. A motion of an amicus curiae to participate in the oral argument will be granted only for extraordinary reasons. The same number of copies of the brief of an amicus curiae shall be filed with the clerk and served on counsel for each party separately represented as required by Rule 19(b) .

Amended October 30, 1997, effective January 1, 1998.