The Financial Industry Regulatory Authority has fined Merrill Lynch $500,000 for failing to file or promptly file certain required disclosures that the self-regulatory organization argues resulted in hidden investment risks and possible harm to investors.

During a span of six years, from 2005 through August 2011, Merrill Lynch mishandled the filing of 1,200 disclosures, according to FINRA. Those disclosures included arbitrations, civil lawsuits, customer complaints and registration records to disclose the hiring and termination of its brokers.

The firm either did not file those disclosures on time or did not file them at all, FINRA stated. That includes convictions, felony charges and settlements involving brokers. It also includes the registrations and terminations of brokers. Notice for those events is typically required within 30 days.

"Firms that fail to file important regulatory information in a timely manner can compromise the integrity of CRD (Central Registration Depository) and BrokerCheck," FINRA Executive Vice President and Chief of Enforcement Brad Bennett said in a statement. "In this instance, Merrill Lynch failed to report critical information that regulators and investors rely upon. Without timely and accurate reporting by firms, investors only have part of the picture when researching and making decisions about their brokers."

Merrill Lynch neither admitted nor denied the charges, according to a letter of consent sent by the firm to FINRA. "As part of a review that began in 2009, Merrill Lynch identified instances where the firm had not made regulatory filings in a timely manner," Merrill Lynch spokesman Bill Halldin said Monday. "We have enhanced our policies and procedures to address issues raised in this matter and to ensure that client complaints are properly reported."

In its investigation, FINRA found that from 2007 to 2011, Merrill Lynch mishandled a total of 650 reports by either not filing to disclose those events, including customer complaints and settlements, or by not filing those disclosures on time. From 2005 through 2011, Merrill Lynch either neglected or did not file those disclosures in a timely manner from 23% to 63% of the time, FINRA stated.

Merrill Lynch also either did not file or file within regulatory deadlines about 300 arbitrations and civil and customer complaints, according to FINRA's investigation. Merrill Lynch failed to file 100% of the time from July 2007 through June 2009 and from October 2009 through February 2010. And the firm did not file forms related to broker registration and termination (forms U4 and U5) from 28% to 79% of the time between 2007 and 2010, FINRA said.

Merrill Lynch also did not react promptly to about 300 customer complaints, FINRA said, due to its failure to adequately prepare its employees to handle that responsibility and have systems ready for the increased number of grievances it received.