17 C.F.R. § 240.19c-1
The rules of each national securities exchange shall provide as follows:
No rule, stated policy, or practice of this exchange shall prohibit or condition, or be construed to prohibit or condition or otherwise limit, directly or indirectly, the ability of any member acting as agent to effect any transaction otherwise than on this exchange with another person (except when such member also is acting as agent for such other person in such transaction), in any equity security listed on this exchange or to which unlisted trading privileges on this exchange have been extended.
17 C.F.R. §240.19c-1
Secs. 2 , 3 , 6 , 11 , 17 , 19 , 23 , Pub. L. 78-291 , 48 Stat. 881, 882, 885, 891, 897, 898, 901, as amended by secs. 2 , 3 , 6 , 14 , 16 , 18 , Pub. L. 94-29 , 89 Stat. 97, 104, 110, 137, 146, 155 (15 U.S.C. 78b , 78c , 78f , 78k , 78q , 78s , 78w , as amended by Pub. L. 94-29 (June 4, 1975)); sec. 7 Pub. L. 94-29 , 89 Stat. 111 (15 U.S.C. 78k-1 )