Looking for a TAR clause

All, I need your assistance locating a TAR clause.  I'm trying to validate the following statement and I can't find the TAR clause it ties back to:

           "The TAR allows contracting officers to exceed the contract maximum value up to 20%"

Is it a correct statement?  If it is, what is the source TAR clause?

I have researched this topic for the past 2 hours and I'm coming up short. 

Thanks!

Shauna