With regard to the additional guarantee regarding the quality of construction work, provided by the contractor at the request of the contracting authority, interpretation difficulties have long persisted, due to the lack of independent statutory regulation. Although the view has become established in Polish law that the provisions on sales guarantees (Article 577 et seq. of the Civil Code) should be applied by analogy to matters not covered by the guarantee document, the CJEU found that the principle of equal treatment of competitors, along with the obligation to ensure sufficient transparency in public procurement procedures, precludes the application by analogy to construction contracts of national law provisions regulating sales guarantees, the content of which was not expressly referred to in advance in either the tender documentation or the construction contract.

The issue of claims for damages for the unjustified exclusion of a contractor from applying for a public contract still poses many interpretation difficulties on the basis of the European principle of effective liability of the contracting authority – tender organiser for the consequences of procedural irregularities committed. The framework for compensation claims in the Remedies Directive does not address many issues that fall within the domain of national law from the perspective of the above principle. A recent Tribunal EU judgment identified the need to interpret the conditions and limits of a contracting authority’s liability for depriving a competitor of a realistic chance of winning a contract. The views of the Tribunal and their developed argumentation may be important for the interpretation of Polish normative solutions.

The boundaries of permissible modifications and additions in public procurement contracts pose many difficulties of interpretation, both in practice and in jurisprudence, especially against the background of the normative concept of "material modifications to the contract" prohibited by European directives. The commented judgment of the CJEU directly relates to the possibility of extending a deadline for an execution of a public contract, as well as the permissible use in this regard of an ordinary electronic form, despite the general requirement of a written form for a basic contract. The findings and views of the Tribunal, together with the developed legal argumentation, are of momentous significance for the application of Polish law.

The formulation of contractual penalties in public procurement still encounters numerous qualification-related difficulties, related in particular to the selection of the title of the penalty adequate to the breach of contractual obligations and the optimization of its amount. Their rationalization is justified not only by the protection of public interests and the public law obligation to pursue claims, but also by the common idea of contractual justice. Recently, there have been increasing difficulties in interpreting the new provisions against abusive clauses, introduced unjustifiably to the disadvantage of contractors to adhesively designed public procurement contracts, subject to appeal review before the National Chamber of Appeals. Interpretation uncertainties regarding the permissible accumulation of penalties under various titles and the mandatory determination of the maximum limit of all penalties are also significant. The purpose of this article is to explain these difficulties, combined with a proposal for a functional interpretation of the questionable provisions.

The admittance of substitute performance of a contracted service by a third party at the contractor's expense, as a type of fulfilment of the debtor's financial liability, especially in the event of falling into delays or the defective performance of a public contract, constitutes the reinforcement of the principle of real performing a contract, which is important from the point of view of the effective satisfaction of public needs. The alternative form of liability being the rescission of the contract by the contracting authority, while retaining the right to compensation or demanding the payment of a contractual penalty does not always sufficiently satisfy its interests. The authorization of the contracting authority to apply substitute performance can arise directly from the Act, although it only applies to rare, exceptional situations, or a court order. The significance of an authorization arising from a previous contractual provision has recently been increasing. However, this basis poses difficulties of qualification, primarily of a structural nature. The principle of the real performance of a contract can also be implemented by filing an action against an unreliable contractor for a performance in kind, although enforcement difficulties can be avoided by a court order authorizing substitute performance by a third party at the contractor's expense.