... through a collection agency, can the companies take my tax refund?

:(

Possibly, but NOT likely.

To get your federal tax refund, the collection agency has to get a local court order, THEN go through federal court, THEN apply to the IRS to get a garnishment.

That takes a LONG time, and is probably only good for one year, because the taxpayer, noticing that he stop getting his refund and being told WHY by the IRS, would just adjust his withholding to PAY a small amount when he filed.

For this reason, most private collection agencies do not bother.