; or (ii) the complaining party makes the demonstration described in subparagraph (C) with respect to an alternative employment practice and the respondent refuses to adopt such alternative employment practice. (B) Demonstration of causation (i) Particular employment practices With respect to demonstrating that a particular employment practice causes a disparate impact as described in subparagraph (A)(i), the complaining party shall demonstrate that each particular challenged employment practice causes a disparate impact, except that if the complaining party can demonstrate to the court that the elements of a respondent's decisionmaking process are not capable of separation for analysis, the decisionmaking process may be analyzed as one employment practice. (ii) Demonstration of noncausation If the respondent demonstrates that a specific employment practice does not cause the disparate impact, the respondent shall not be required to demonstrate that such practice is required by business necessity. (C) Alternative employment practice The demonstration referred to by subparagraph (A)(ii) shall be in accordance with the law as it existed on June 4, 1989, with respect to the concept of alternative employment practice . (2) Business necessity no defense to intentional discrimination A demonstration that an employment practice is required by business necessity may not be used as a defense against a claim of intentional discrimination under this section. (3) Rules concerning controlled substances Notwithstanding any other provision of this section, a rule barring the employment of an individual who currently and knowingly uses or possesses a controlled substance, as defined in section 102(6) of the Controlled Substances Act ( 21 U.S.C. 802(6) ) and included in schedule I or II of the schedules specified in that section, other than the use or possession of a drug taken under the supervision of a licensed health care professional, or any other use or possession authorized by the Controlled Substances Act ( 21 U.S.C. 801