A contractor receiving an operating-differential subsidy, or a charterer under chapter 575 of this title, may not continue as a party to or conform to an agreement with another carrier by water, or engage in a practice in concert with another carrier by water, that is unjustly discriminatory or unfair to any other citizen of the United States operating a common carrier by water employing only vessels documented under the laws of the United States on an established trade route from and to a United States port.

No payment or subsidy of any kind may be paid, directly or indirectly, out of funds of the United States Government to a contractor or charterer that has violated subsection (a).