Are underpayment penalty and interest (state MI) deductible in year paid (ie 2015 penalty paid in 2016)?

[MaryK1]

No, penalty and interest for state income taxes are not deductible but the amount you paid for the tax is.

[obcraig1]

Any chance we can get the source indicating that interest assessed for underpayment of a prior year's state income tax is not deductible?  While I agree, the CPA says that this is wrong (i.e., he claims that the interest assessed and paid for underpayment of prior year state income taxes IS deductible).  Would love to have a section of the IRC, and IRS Revenue Ruling, Instructions, or any other source to refer the CPA to!