The IRS uses Notice CP14 to inform you of a balance due. There are also 2 new Notices: 1) CP14H which bills you for not having health insurance & 2) Notice CP14I, which bills you for excess IRA contributions. The IRS also could send Form 3552.
Your situation is not yet urgent but should be corrected. The IRS will send gradually more hostile letters to you until they issue a Notice of Intent to Levy. If you can't pay the amount quickly, don't call the IRS until you get legal advice.
If You Owe
For small tax debts (under $25,000) you may simply divide what you owe by 72 (the bankruptcy time period) and that will be your monthly payment. (See Form 9465)
If You Can't Pay
But, if you can't pay, they will often require a Form 433A or Form 433F (not both) to disclose your income, expenses, assets & liabilities. One of these forms must be completed by you, and only you, because you have access to all of the information. It takes a lot of work & you need Tax Attorney guidance along the way. Our webinars show you the tricks and tactics of preparing these forms while the Collection Prep Steps get you prepared for the IRS!