In this paper we concentrate mainly on the notion of β-pregroups, which are pregroups enriched with modality operators. β-pregroups were first proposed by Fadda [11] in 2001. The motivation to introduce them was to limit the associativity in the calculus considered. In this paper we present this new calculus in the form of a rewriting system, prove the very important feature of this system - that in a given derivation the non- expanding rules must always proceed non-contracting ones in order (...) the derivation to be minimal. We also propose a sequent system for this calculus and prove the cut elimination theorem for it. As an illustration we show how to use β-pregroups for linguistical applications. (shrink)