Many U.S. states recognize a duty of good faith and fair dealing that may not be waived and is part of every contract.
In Colorado, this duty applies to the manner in which a party to a contract with discretionary rights under a contract is required to exercise those rights. This must be done in a manner consistent with the mutual intent of the parties in entering into the contract. It is implied as a matter of law in all contract and even sophisticated parties (e.g. big oil companies in business to business transactions) can't waive it.
Colorado's leading case on the topic is Amoco Oil Co. v. Ervin, 908 P.2d 493 (Colo. 1995) which spells out the doctrine at length:
Colorado, like the majority of jurisdictions, recognizes that every
contract contains an implied duty of good faith and fair dealing. §
4-1-203, 2 C.R.S. (1992) ("Every contract or duty within this title
imposes an obligation of good faith in its performance or
enforcement."); see, e.g., Wells Fargo Realty Advisors Funding, Inc.
v. Uioli, Inc., 872 P.2d 1359, 1362 (Colo.App.1994); Friedman v.
Colorado Nat'l Bank, 825 P.2d 1033, 1042 (Colo.App.1991), rev'd on
other grounds, 846 P.2d 159 (Colo.1993); Ruff v. Yuma County Transp.
Co., 690 P.2d 1296, 1298 (Colo.App. 1984); see also Larese v.
Creamland Dairies, Inc., 767 F.2d 716, 717 (10th Cir.1985)
(explaining that the franchisor-franchisee relationship is one that
requires the parties to deal with one another in good faith and in a
commercially reasonable manner); see generally Restatement (Second) of
Contracts § 205 (1981); 3 Arthur Linton Corbin, Corbin on Contracts §
561, at 278 n. 2 (1960); Steven J. Burton, Breach of Contract and the
Common Law Duty to Perform in Good Faith, 94 Harv.L.Rev. 369, 369
(1980) [hereinafter Burton I].
The good faith performance doctrine is generally used to effectuate
the intentions of the parties or to honor their reasonable
expectations. See State Farm Mut. Auto. Ins. Co. v. Nissen, 851 P.2d
165, 168 (Colo. 1993); Davis v. M.L.G. Corp., 712 P.2d 985, 989
(Colo.1986); Steven J. Burton, More on Good Faith Performance of a
Contract: A Reply to Professor Summers, 69 Iowa L.Rev. 497, 499 (1984)
[hereinafter Burton II]. Good faith performance of a contract involves
"faithfulness to an agreed common purpose and consistency with the
justified expectations of the other party." Wells Fargo, 872 P.2d at
1363 (citing Restatement (Second) of Contracts § 205 cmt. a (1981)).
The application of the reasonable expectations doctrine often "fails
to give effect to some hornbook rules governing the construction of
contracts," including "the precept that contracts which are free from
ambiguity are to be enforced as written...." Davis, 712 P.2d at 990
& n. 7. Nonetheless, adherence to this principle promotes "the central
policy underlying contract law, that of construing contracts so as to
effectuate the parties' intentions...." Id. at 991; see also State
Farm, 851 P.2d at 166-67; Simon v. Shelter Gen. Ins. Co., 842 P.2d
236, 240 (Colo.1992).
The duty of good faith and fair dealing applies when one party has
discretionary authority to determine certain terms of the contract,
such as quantity, price, or time. Hubbard Chevrolet Co. v. General
Motors Corp., 873 F.2d 873, 876 (5th Cir.), cert. denied, 493 U.S.
978, 110 S. Ct. 506, 107 L. Ed. 2d 508 (1989); Burton II, supra,
at 501. The covenant may be relied upon only when the manner of
performance under a specific contract term allows for discretion on
the part of either party. See Hubbard Chevrolet Co., 873 F.2d at
877. However, it will not contradict terms or conditions for which a party has bargained. Id.
The concept of discretion in performance "refers to one party's power
after contract formation to set or control the terms of performance."
Burton II, supra, at 501. Discretion occurs when the parties, at
formation, defer a decision regarding performance terms of the
contract. Id. Generally, the good faith performance doctrine may be
used to protect a "weaker" party from a "stronger" party. Weakness and
strength in this context, however, do not refer to the relative
bargaining power of the parties. One commentor explained:
"Good faith performance cases typically involve arm's-length
transactions, often between sophisticated business persons. The
relative strength of the party exercising *499 discretion typically
arises from an agreement of the parties to confer control of a
contract term on that party. The dependent party then is left to the
good faith of the party in control."
Burton I, supra, at 383-84.
A right to terminate a contract for convenience is a discretionary right under a contract that is nominally absolute. But, if that right were exercised in a manner calculated to harm the other party to the contract rather than primarily to allow a party to end a contractual relationship that had become burdensome or undesirable, that might breach the implied duty of good faith and fair dealing in the contract.