It is well-known that medium access control (MAC) protocols are vulnerable to the selfish behavior of nodes, which often results in inefficient use of resources. In this work, we aim to overcome this inefficiency by constructing a class of defection-proof MAC protocols in the context of slotted multiple access communications. The operation of the proposed protocols can be divided into a review phase and a reciprocation phase. In a review phase, nodes cooperate and collect signals on the behavior of other nodes. At the end of a review phase, nodes perform a statistical test independently to determine whether there has been a defecting node in the system. In a reciprocation phase, a node cooperates if it concludes that no defection has occurred and carries out a punishment otherwise. We provide sufficient conditions for protocols to be defection-proof against a constant defection strategy and to achieve an arbitrarily small efficiency loss. We analyze an example of a statistical test based on which we can build protocols that satisfy the sufficient conditions.