Is Form 4137 for reporting hidden income?

[Strongsilence-CPA]

IRS instructions:  Tax owed on tips you did not report to your employer, including any allocated tips shown on your Form(s) W-2 that you must report as income. 

Bold is mine. Is it odd that the IRS states this? Are they really asking for unreported income? 

I rarely get service and tip workers so I really don't know.

Edit:  I am going to assume that my client reported all her tips to her employer.  So, I think column d should report the same amount as column c.

Am I missing something important?

[Strongsilence-CPA]

I see that the W-2 box 7 number was mistakenly input by me as Box 8. Thus F4137 was produced.

Channeling Emily Latella --- "never mind"

[IRonMaN · Accepted solution]

Another mystery solved.  Now on to Bigfoot and the Loch Ness Monster.

[sjrcpa]

There is, or was, some rule along the lines of tips of less than $20 in a month don't have to be reported to employer. It was a Long Time Ago I dealt with this, when $20 bought something, so it may not be accurate now.