If you fall behind on paying your taxes, you will end up with tax debt that the government will keep trying to collect. You cannot get rid of this debt through bankruptcy, so you have to take it seriously.
The IRS is not in the business of trying to collect the debt you owe. According to the IRS, it passes this job to private debt collection companies.
Congress gave the IRS the right to use debt collection companies through the passage of a law. It is completely legal and the only way the IRS will handle overdue tax debt that meets specific requirements.
The IRS will originally do the debt collecting. It will attempt to contact you and set up a payment plan or come to an agreement to resolve the debt. If this fails, the IRS may send your account to a collection agency after a year with no contact with you.
You can delay or avoid a private debt collector getting your overdue tax account by staying in contact with the IRS. There are some situations that will allow you to prevent them from turning over your account. For example, if you were a victim of identity theft that impacted your taxes, communicate this with them and it will stop the collection transfer.
The IRS always sends you a letter to let you know your debt is going to a debt collection agency. You should try to avoid this situation, if possible, by working on a payment plan. It can make it easier for you to repay the debt without hassle.