The Notice LT16 informs you that there is a balance due (money you owe the IRS) on one of your tax accounts and tells you how much you owe, when it’s due, and how to pay and/or it informs you that you have unfiled tax returns due.
If you can’t pay the full amount by that date, you need to figure out what payment options might work for your situation, and act to set up a payment plan or discuss other ways to pay off your balance. Being proactive in addressing the tax debt may prevent additional penalty and interest charges and eliminate the need for the IRS to take action to collect the balance, learn more on I got a notice from the IRS.
If you choose not to respond to the Notice LT16, the IRS may send further taxpayer collection notices to you requesting payment for the tax balance owing. The IRS may also file a Notice of Federal Tax Lien or issue a levy.