Employer organisations in the metal and electrical industry (M+E) first began to offer membership to firms not participating in collective bargaining in the 1990s. Taking into account central theoretical approaches, this article asks to what extent this „ohne Tarifbindung“ (OT – not covered by collective agreements) membership strategy has had a stabilizing or destabilizing effect on the collective bargaining system. Besides a regional analysis of OT development and structures, an evaluation of expert interviews with M+E employer associations and a company survey form the basis of this study. While employers in principle support the advantages of sector-level agreements, the acceptance of core regulations (pay levels, working time volume) has declined. From the perspective of employer associations, the OT structures are a necessary means to organize SMEs. Since the mid-2000s, the collective bargaining coverage of employees in the metal and electrical industry has stabilised. These opening clause developments, however, have resulted in increasing flexibility and differentiation within the collective bargaining system. In some collective bargaining regions, employer associations have used the OT as a strategic means to exert pressure on the IG Metall. Although the social partners have been able to reach pragmatic agreements, especially in times of crises, these conflicting strategies on the part of both parties point to a stabilisation process built on clay feet.