That kind of “give us anything you can” approach is common among consumer debt collectors, but the government has typically been more measured, weighing what is owed against what the taxpayer can reasonably afford. When taxpayers cannot pay their entire bill at once, the I.R.S.’s internal collectors are generally only permitted to place them into installment plans that will fully resolve their debt.

The idea is that pushing taxpayers to the limit, while temporarily good for the I.R.S., causes long-term strain on the government over all. No one wins, the theory goes, when taxpayers wind up on public assistance from settling overdue tax bills. The I.R.S. does not try to collect from people who make only enough to afford basic living expenses like food, housing and transportation. (Only one collector, Performant, had lines in its scripts about how to handle hardship cases. Those accounts should be marked and returned to the I.R.S., Performant instructed its employees.)

Low-income taxpayers make up most of the cases farmed out to the private collectors, according to an analysis by Ms. Olson. After reviewing the first batch of files the I.R.S. sent to outside collectors, her office found that nearly a quarter of the accounts involved taxpayers with below-poverty level wages, and more than half were taxpayers with incomes of less than 250 percent of the poverty level.

Ms. Olson said she was “deeply concerned” by collectors suggesting that taxpayers borrow against their retirement savings, take out home loans or increase their other debts to pay their taxes.

“The I.R.S. may suggest those things, but the I.R.S. is authorized to perform a financial analysis of a taxpayer’s ability to pay, and it does not collect from taxpayers where its financial analysis shows doing so would impose a financial hardship,” she said by email.

Pioneer, a subsidiary of Navient, was effectively fired two years ago by the Education Department from its contract to collect overdue student loan debt after the agency determined that it gave borrowers inaccurate information about their loans at “unacceptably high rates.” Pioneer was sued this year by the Consumer Financial Protection Bureau, which said it “systematically misled” borrowers.

Navient is fighting the consumer bureau’s lawsuit and has denied any wrongdoing. It declined to comment on its tax debt collection efforts, referring questions to the I.R.S. The other three collectors did not respond to questions about their call scripts.