From OSHA:
The following press release was recently issued by OSHA to help employers better understand how to respond when OSHA instigates a whistleblower complaint investigation. On average, 20% of all OSHA enforcement inspections are triggered by employee complaints, but that number has risen to 23% in the last couple of years.
This number has risen because OSHA takes employee workplace health and safety complaints very seriously and are mandated to respond to each and every complaint. They have a review process to evaluate the validity of the complaint and level of threat of hazards, but will always respond either with an actual inspection or via fax. In either case, employers need to respond and remediate any identified hazards.

It’s also a reminder that employers must always take complaints seriously, fully investigate, and take steps to correct problems. And just as importantly, NEVER RETALIATE against employees for complaining or face serious consequences.

OSHA has updated its Whistleblower Investigation Manual* to help employers, workers and their representatives understand the investigative process and how to request documents from OSHA during and after an investigation. The new material affirms that the standard for all whistleblower investigations is whether there is “reasonable cause to believe” that a violation occurred. The manual also provides guidance on disclosure requests under the Freedom of Information Act and the Privacy Act.
OSHA enforces the whistleblower protection provisions of the OSH Act and 21 other statutes protecting workers who report violations of laws in various industries. In fiscal year 2015, OSHA helped award more than $25 million to whistleblowers across the country – a reminder to employers that workers have a right to speak up, without fear of retaliation, when they believe that their safety and health is at risk.