Do not just send them a
payment. Contact the IRS first, and you may want to elicit the help of a CPA in
your hometown.
The notice should give you specific reasons as to where the
change is coming from. It could be a decrease in your deductions,
or an increase in your income (maybe you inadvertently left off income you
didn't know about) etc...
Contact the IRS at the number listed on the notice and get them
to explain any decrease in a deduction (or expense). Be ready to provide them
with any documentation that they need. Just because the IRS says that they
disagree with one of your deductions (or expenses) does not mean that you have
to agree with their disagreement. Which is why it may be a good idea to get a
local CPA involved.
If you did inadvertently forget to include any income, there may
be little you can do. In this case, if you can show that you did not leave the
income off in an attempt to skirt your responsibilities, then you should be
able to get the IRS to abate any penalties. However, they will not forgive any
interest due in a situation where you did not include all your income.
Also, the following website is an excellent tool in learning why
the IRS sent you a letter to begin with. The letter you received should have a
identifying number or type of notice (for example it could be a CP05). Use this
number or "identifier" to search for more information.
https://www.irs.gov/individuals/understanding-your-irs-notice-or-letter
