(101)Contracting authorities should further be given the possibility to exclude economic operators which have proven unreliable, for instance because of violations of environmental or social obligations, including rules on accessibility for disabled persons or other forms of grave professional misconduct, such as violations of competition rules or of intellectual property rights. It should be clarified that grave professional misconduct can render an economic operator’s integrity questionable and thus render the economic operator unsuitable to receive the award of a public contract irrespective of whether the economic operator would otherwise have the technical and economical capacity to perform the contract. Bearing in mind that the contracting authority will be responsible for the consequences of its possible erroneous decision, contracting authorities should also remain free to consider that there has been grave professional misconduct, where, before a final and binding decision on the presence of mandatory exclusion grounds has been rendered, they can demonstrate by any appropriate means that the economic operator has violated its obligations, including obligations relating to the payment of taxes or social security contributions, unless otherwise provided by national law. They should also be able to exclude candidates or tenderers whose performance in earlier public contracts has shown major deficiencies with regard to substantive requirements, for instance failure to deliver or perform, significant shortcomings of the product or service delivered, making it unusable for the intended purpose, or misbehaviour that casts serious doubts as to the reliability of the economic operator. National law should provide for a maximum duration for such exclusions. In applying facultative grounds for exclusion, contracting authorities should pay particular attention to the principle of proportionality. Minor irregularities should only in exceptional circumstances lead to the exclusion of an economic operator. However repeated cases of minor irregularities can give rise to doubts about the reliability of an economic operator which might justify its exclusion.