The Financial Industry Regulatory Authority (FINRA) will require the use of two new trade reporting modifiers to report transactions exempt from the Securities and Exchange Commission’s “trade-through” rule that would apply to certain transactions (i) to correct bona fide errors in the execution of customer orders, and (ii) that offer print protection to displayed customer orders when trades are reported at prices inferior to such orders. Any such transactions must be in accordance with applicable SEC guidance relating to Regulation NMS Rule 611 to qualify for the trade-through exemptions. The FINRA notice announcing the change included an updated trade reporting modifier chart providing a uniform methodology for reporting trade modifiers including the new additions referenced above. The use of the “error correction” and “print protection” modifiers becomes mandatory under FINRA trade reporting rules on July 1, 2009.  

http://www.finra.org/web/groups/industry/@ip/@reg/@notice/documents/notices/p117992.pdf