24 C.F.R. § 103.205
Where the Assistant Secretary determines that the alleged discriminatory practices contained in a complaint are pervasive or institutional in nature, or that the processing of the complaint will involve complex issues, novel questions of fact or law, or will affect a large number of persons, the Assistant Secretary may identify the complaint for systemic processing. This determination can be based on the face of the complaint or on information gathered in connection with an investigation. Systemic investigations may focus not only on documenting facts involved in the alleged discriminatory housing practice that is the subject of the complaint but also on review of other policies and procedures related to matters under investigation, to make sure that they also comply with the nondiscrimination requirements of the Fair Housing Act.
24 C.F.R. §103.205