In comments to the agency when the rule was proposed, for example, NAMIC said the rule could undermine the underwriting process and "trigger a wave of frivolous litigation."

The rule had no effective date because it was a clarification of what HUD thought it already had the authority to do, NAMIC officials said when the final rule was published.

NAMIC and AIA officials declined comment, referring all calls to Williams and Connolly, the Washington law firm that filed the suit.

The suit argues that interpreting the Fair Housing Act to extend disparate-impact liability to the provision and pricing of homeowner's insurance "requires insurers to consider characteristics such as race and ethnicity and to disregard legitimate risk-related factors."

The lawsuit claims that this interpretation "would require insurers to provide and price insurance in a manner that is wholly inconsistent with well-established principles of actuarial practice and applicable state insurance law."

The suit also contends that, "That is not only a perverse result, but it also flies in the face of the McCarran-Ferguson Act, which entrusts insurance regulation to the states."

The rule was first proposed in late 2011.

NAMIC lobbied extensively against the rule, and even enlisted members of Congress in an effort to put pressure on the agency not to finalize it.

A key concern of NAMIC and other industry lawyers is that the rule ignores the question of intent, meaning that any disparate impact could be treated as discriminatory and subject to penalties or litigation, regardless of how it came about."

A key argument by insurers is that risk differentiation is essential to the insurance business and pricing that unintentionally produce statistical disparities bears no resemblance to discrimination based on race, color, religion, sex, or disability.