Some Nasdaq market makers have also worked improperly <br /> together in this way to fill customer orders or to reduce <br /> inventory exposure.-- In such cases, a market maker <br /> having a sizeable customer order or an inventory imbalance called <br /> upon other market makers to coordinate their quotations and <br /> transactions with the requesting market maker. The fact that a market maker used these arrangements when engaged in buying or selling securities for a customer was typically not disclosed and may have violated the duties owed by the market maker to its customer. <br /> <br /> Such undisclosed collaboration can injure the interests of <br /> both retail and institutional investors. A market maker <br /> representing a customer order is required to obtain the most <br /> favorable terms for its customer that are available under the <br /> circumstances. See, e.g., Opper v. Hancock Securities (Supplied by us: Opper v. Hancock Securities Corporation, 250 F. Supp. 668 (S.D.N.Y. 1966)).