The presented paper will focus on the extent of requirements of EU law for nullity or ineffectiveness of contracts in specific areas linked to functioning internal market: competition law, including agreements restricting competition, abuse of dominant position, merger control and state aid, and rules of public procurement. The scope of EU-law-based nullity is quite limited and only Art. 101(2) TFEU provides expressed nullity of agreements restricting competition. In the case of abuse of dominance, nullity of contract constituting abuse of dominant position can be drawn from the principle of effectiveness of EU law. Validity or nullity of contracts violating suspension clause in merger control regime are assessed in two periods - before decision on merger and after decision of the Commission. State aid regime cannot rely on EU-law-based nullity of contracts that violate EU state aid rules. Finally, public procurement rules appear the most complex in this context since they operate with the "right" of the contracting authority to terminate contract and power of revision authority to declare "ineffectiveness" of illegally awarded contract, and therefore revision of directives is suggested.