OK, I appreciate the additional information.
The traditional term associated with this practice is "kickback", as you no doubt are familiar. It is the same whether in the private or public sectors. Clearly, the public sector situation provides for criminal sanctions.
With private companies, the kickback money may or may not be criminally liable. On the one hand, many companies allow this to take place as part of a employee's compensation, a form of commission. On the other, a ccould argue that you are benefitting illegally from the work derived through the business, a form of embezzlement. Now, that still doesn't mean it would necessarily be a criminal act.
Given your question and the additional information, it seems clear that the company would frown upon the payments. So, it comes down to what you would like to do. If it is possible, you might consider talking to the company and telling them what has happened, and then offer to pay the money over to them. Another approach may be to terminate the payments completely, pay the monies back to the sub-contractor, and simply move on with business as usual.
In sum, it is not certain that the receipt of the monies would be criminal. There could be a basis for a civil action by the company. How you proceed depends upon dozens of other questions. As such, you need to discuss the above information with a good criminal attorney in your area. There is no substitute for that. You should try to find one through reputation, not advertising.
I hope this helps.
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