79 It is true that Article 3(7) of Directive 96/71 provides that paragraphs 1 to 6 are not to prevent application of terms and conditions of employment which are more favourable to workers. In addition, according to recital 17, the mandatory rules for minimum protection in force in the host country must not prevent the application of such terms and conditions.
80 Nevertheless, Article 3(7) of Directive 96/71 cannot be interpreted as allowing the host Member State to make the provision of services in its territory conditional on the observance of terms and conditions of employment which go beyond the mandatory rules for minimum protection. As regards the matters referred to in Article 3(1), first subparagraph, (a) to (g), Directive 96/71 expressly lays down the degree of protection for workers of undertakings established in other Member States who are posted to the territory of the host Member State which the latter State is entitled to require those undertakings to observe. Moreover, such an interpretation would amount to depriving the directive of its effectiveness.
81 Therefore – without prejudice to the right of undertakings established in other Member States to sign of their own accord a collective labour agreement in the host Member State, in particular in the context of a commitment made to their own posted staff, the terms of which might be more favourable – the level of protection which must be guaranteed to workers posted to the territory of the host Member State is limited, in principle, to that provided for in Article 3(1), first subparagraph, (a) to (g) of Directive 96/71, unless, pursuant to the law or collective agreements in the Member State of origin, those workers already enjoy more favourable terms and conditions of employment as regards the matters referred to in that provision.
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110 However, collective action such as that at issue in the main proceedings cannot be justified in the light of the public interest objective referred to in paragraph 102 of the present judgment, where the negotiations on pay, which that action seeks to require an undertaking established in another Member State to enter into, form part of a national context characterised by a lack of provisions, of any kind, which are sufficiently precise and accessible that they do not render it impossible or excessively difficult in practice for such an undertaking to determine the obligations with which it is required to comply as regards minimum pay (see, to that effect, Arblade and Others, paragraph 43).