Assuming that your contribution is being made in a timely manner, check the total withheld from your paycheck for a quarter or year against the total of the corresponding statement, Kmak said.

If there's any sort of discrepancy or error, bring it to your employer's attention, Wray said. If the employer refuses to act, you should call the Labor Department helpline for assistance.

For his part, Reish said another warning sign is if you don't get a quarterly statement in a timely manner. The Labor Department has on its website other warning signs that your 401k contributions are being misused.

Ask for auditor's report

If you want to do additional due diligence before contacting your employer or the Labor Department, Kmak recommends that you ask your employer for the auditor's report from the Form 5500, which is only available if the plan has more than 100 participants. The 5500 is the official form that the retirement plan files with the Labor Department.

Experts say you should learn what your plan fiduciary's responsibilities are and what recourse you might have if they don't follow the required conduct standards. For instance, "if the plan lost money because of a breach of their duties, fiduciaries would have to restore those losses, or any profits received through their improper actions," the Labor Department said on its website.

And if an employer did not forward participants' 401k contributions to the plan, the company would have to pay back the contributions to the plan as well as any lost earnings, and return any profits improperly received.

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After you call the Labor Department, it will conduct an investigation and, according to Wray, if regulators find that there has been an error or misappropriation it will intervene. In some cases, there could be a civil or a criminal action.

Another option if you suspect wrongdoing is to file a lawsuit against your employer. "Recently, the Supreme Court clarified that an individual 401k participant with a grievance can do so," said Wray.

What happens to your 401k money is up to you. You are the watchdog. You are your own advocate. Yes, the Labor Department will conduct an audit. But only after you contact them. They are relying on you to contact them. It's not the other way around.