In this paper, we propose IAMAC, an Interference Avoidance MAC protocol to avoid inter-node interference in dense wireless sensor networks. IAMAC interacts with routing protocol via cross-layer information sharing between the MAC and network layer. By providing information from network layer, we enable the MAC protocol to make proper decisions which result in fewer inter-node interference and lower delay. Through interference avoidance, IAMAC reduces energy consumption per node and leads to higher network lifetime compared with S-MAC and Adaptive S-MAC. In addition, IAMAC has lower delay than S-MAC. In our evaluations, we considered IAMAC in conjunction with two error recovery methods (ARQ and Seda). Our simulation results show that our protocol is highly compatible with Seda and this integration achieves higher network throughput and lifetime.