The opening line of IRS Notice CP503 states, "Second reminder: You have unpaid taxes for [year]". The IRS uses this notice to inform you for the 2nd time that they expect payment of past due taxes. Your situation is not yet urgent but needs correction by the tax attorney. There is also a Notice CP503K & a Notice CP503H, concerning Health Care Tax liability.
The IRS is required to give you notice that they intend to seize, or take, your possessions, including your wages, house, bank accounts, etc. This is called a "Notice of Intent to Levy". The CP503 is not a Notice of Intent to Levy but it's the one just prior to it.
The next notice from the IRS will likely be the Notice CP504, Notice of Intent to Levy. So, it's best to take care of this problem prior to the IRS seizing your wages or property. Please follow the Prep Steps for IRS Notice CP503 and see Mr. Hopkins in Colorado Springs, Pueblo or Denver before proceeding!
Essentially, the IRS will want to know how much you can afford to pay. So, in most cases, you'll be required to complete Form 433-A or Form 433F to disclose your income & assets. These forms are signed under penalty of perjury so they must be carefully completed and you must gather the evidence to support each entry on the form.
Please take our TaxHelp Webinars to learn the tricks & traps of completing these forms!