The Company, on the other hand, cites a number of cases which hold that notice to modify does not constitute termination. See Motor Carriers Council of St. Louis, Inc. v. Local Union No. 600, 8 Cir., 1973, 486 F.2d 650; International Union of Operating Engineers v. Dahlem Construction Co., 6 Cir., 1951, 193 F.2d 470; Texoma Natural Gas Co. v. Oil Workers International Union, Local No. 463, N.D.Tex., 1943, 58 F. Supp. 132, aff'd 5 Cir., 1944, 146 F.2d 62, cert. denied, 324 U.S. 872, 65 S.Ct. 1017, 89 L.Ed. 1426 (1945); United Steel Workers v. Shakespeare Co., W.D.Mich., 1949, 84 F. Supp. 267; Mountain States Division No. 17 v. Mountain States Telephone Telegraph Co., D.Colo., 1948, 81 F. Supp. 397. The Company asserts that these cases stand for the proposition that an effective notice of termination must be clear, explicit, and unequivocal. Furthermore, the Company places great weight on the changes in language incorporated into the 1967 agreement at the Union's request.

The notices did not express an intent to terminate, and this consequence would follow only if other contract provisions are applicable and require it. As we said in International Union of Operating Engineers, Local No. 181 v. Dahlem Construction Co., 193 F.2d 470 (6th Cir. 1951): "A notice to terminate must be clear and explicit. . . . A notice of modification is not a notice of termination and does not affect termination of the contract.

"Since this was a suit for violation of a collective bargaining contract within the purview of § 301(a) of the Labor Management Relations Act of 1947, the pre-emptive doctrine of cases such as San Diego Building Trades Council [etc.] v. Garmon, 359 U.S. 236 [79 S.Ct. 773, 3 L.Ed.2d 775], based upon the exclusive jurisdiction of the National Labor Relations Board, is not relevant. See Local 4264, United Steelworkers v. New Park Mining Co., 273 F.2d 352 (C.A. 10th Cir.); Independent Petroleum Workers v. Esso Standard Oil Co., 235 F.2d 401 (C.A. 3d Cir.); see generally Lodge No. 12, [Int'l] District No. 37, Int'l Assn. of Machinists v. Cameron Iron Works, Inc., 257 F.2d 467 (C.A. 5th Cir.); Local 598, Plumbers Steamfitters Union [Local No. 598] v. Dillion, 255 F.2d 820 (C.A. 9th Cir.); Local 181, Int'l Union of Operating Engineers v. Dahlem Constr. Co., 193 F.2d 470 (C.A. 6th Cir.). As pointed out in Charles Dowd Box Co. v. Courtney, 368 U.S. [502] at 513 [82 S.Ct. 519, 7 L.Ed.2d 483], Congress `deliberately chose to leave the enforcement of collective agreements "to the usual processes of the law."

The relevant question, in both cases, is whether the parties who initiated the modification negotiations intended to let the existing agreement lapse. As we said in International Union of Operating Engineers, Local No. 181 v. Dahlem Construction Co., 193 F.2d 470 (6th Cir. 1951): "A notice to terminate must be clear and explicit. . . . A notice of modification is not a notice of termination and does not affect termination of the contract." 193 F.2d at 475.

Such provisions are common in collective bargaining agreements. See, e.g., International Union of Op. Eng. v. Dahlem Const. Co., 193 F.2d 470, 473 (6th Cir 1951) ("Should such notice of a desire to modify the terms of this agreement be given by either party to the other, then this agreement shall remain in full force and effect until modified by a new agreement resulting from the negotiations"); Paterson v. Parchment P. Co. v. International Brotherhood, 191 F.2d 252, 253 (3d Cir 1951) ("should there be a delay in negotiating the new agreement, this agreement shall remain in full effect until such time as a new agreement is completed"), cert den 342 U.S. 933 (1952). Significantly, the agreement did not contain a "continuation clause" providing that the agreement would remain in effect during negotiations that follow a notice to amend, until modified by a new agreement.

Although we conclude the unions' requests to meet and confer did not constitute notice of intent to terminate the MOU's, City's November 1993 letters presenting its last, best and final offer after the parties bargained to impasse constituted adequate, reasonable notices of termination. (6) Notices to terminate must be clear and explicit, as a notice of modification does not constitute a notice of termination resulting in the cessation of the contract. ( International Union of Op. Eng. v. Dahlem Const. Co. (6th Cir. 1951) 193 F.2d 470, 475.) However, a notice to modify may have the same effect as a notice to terminate where the duration clause within the contract is silent regarding the effect either type of notice would have and essentially treats the notices as functionally equivalent preventing automatic extension.

Since this was a suit for violation of a collective bargaining contract within the purview of § 301(a) of the Labor Management Relations Act of 1947, the pre-emptive doctrine of cases such as San Diego Building Trades Council v. Garmon, 359 U.S. 236, based upon the exclusive jurisdiction of the National Labor Relations Board, is not relevant. See Local 4264, United Steelworkers v. New Park Mining Co., 273 F.2d 352 (C.A. 10th Cir.); Independent Petroleum Workers v. Esso Standard Oil Co., 235 F.2d 401 (C.A. 3d Cir.); see generally Lodge No. 12, District No. 37, Int'l Assn. of Machinists v. Cameron Iron Works, Inc., 257 F.2d 467 (C.A. 5th Cir.); Local 598, Plumbers Steamfitters Union v. Dillion, 255 F.2d 820 (C.A. 9th Cir.); Local 181, Int'l Union of Operating Engineers v. Dahlem Constr. Co., 193 F.2d 470 (C.A. 6th Cir.). As pointed out in Charles Dowd Box Co. v. Courtney, 368 U.S., at 513, Congress "deliberately chose to leave the enforcement of collective agreements `to the usual processes of the law.'"

Most federal courts, however, hold that § 301 created federal substantive rights and, when called upon to choose between state and federal law, apply the latter. E. g., United Electrical, Radio Machine Workers v. Oliver Corp., 205 F.2d 376; Milk Ice Cream Drivers Dairy Employees Union v. Gillespie Milk Products Corp., 203 F.2d 650; Shirley-Herman Co. v. International Hod Carriers Union, 182 F.2d 806; International Plainfield Motor Co. v. Local 343, 123 F. Supp. 683; Waialua Agr. Co. v. United Sugar Workers, 114 F. Supp. 243; Ludlow Mfg. Sales Co. v. Textile Workers Union, 108 F. Supp. 45; Pepper Potter, Inc. v. Local 977, 103 F. Supp. 684; Fay v. American Cystoscope Makers, Inc., 98 F. Supp. 278; Textile Workers Union v. Aleo Mfg. Co., 94 F. Supp. 626; Wilson Co. v. United Packing house Workers, 83 F. Supp. 162; Colonial Hardwood Flooring Co. v. International Union, 76 F. Supp. 493, aff'd 168 F.2d 33; International Union v. Dahlem Const. Co., 193 F.2d 470 (semble); see Rock Drilling, Local Union No. 17 v. Mason Hanger Co., 217 F.2d 687, 691; Schatte v. International Alliance, 182 F.2d 158, 164. Cf. Textile Workers Union v. Arista Mills Co., 193 F.2d 529 (refusal to pass on whether substantive federal rights created; federal law apparently viewed as applicable to issue raised in any event).

Relying on cases from the Sixth Circuit, plaintiffs contend that a notice of termination must be “clear and unambiguous” to be effective. Pls.' Br. at 25 (citing Office & Prof'l Emp. Int'l Union, Local 42, AFL–CIO v. United Auto., Aerospace & Agr. Implement Workers of Am., Westside Local No. 174, UAW, 524 F.2d 1316, 1317 (6th Cir.1975); Int'l Union of Operating Eng'rs, Local No. 181 v. Dahlem Constr. Co., 193 F.2d 470, 475 (6th Cir.1951)). Yet, plaintiffs never explain how this “clear and unambiguous” standard is different from the “timely and unequivocal” standard that the National Labor Relations Board articulated in Retail Assocs., Inc., 120 N.L.R.B. at 393, which we applied in Haas Elec., Inc.

Here, the district court reasonably construed the Union's February 10, 2010 letter as a notice to modify, which does not constitute notice of termination under our law. See Chattanooga Mailers' Union, Local No. 92, 524 F.2d at 1312; Int'l Union of Operating Eng'rs, Local No. 181 v. Dahlem Constr. Co., 193 F.2d 470, 475 (6th Cir.1951). Scassa Asphalt's remaining arguments regarding the termination defense are unavailing. The company contends that “the Union” waited nearly four years to assert that the contracts remained in force and, during that four-year period, the company did not receive “from the Union” a request for payment of delinquent contributions or a request for audit.