Energy efficiency is a key issue because most wireless sensor networks use battery-oriented computing and sensing devices. A network of these devices will collaborate for a common application such as environment monitoring. Thus, energy-efficient MAC protocols have focused on minimizing idle listening time at sensor nodes. Recently, energy-efficient protocols such as S-MAC, B-MAC and EA-ALPL proposed to reduce energy consumption. Here, we propose a cross-layer mechanism called Cross Layer Medium Access Control (CLMAC) protocol that designed for wireless sensor networks. To meet energy-efficient routing, the CLMAC includes routing distance in the preamble field of the B-MAC. Because the CLMAC unified network layer and link layer uses routing distance without big routing table, it enables nodes to reduce control traffic routing overhead. Also, the CLMAC makes it possible to extend the lifetime of the wireless sensor networks that contain a number of nodes. The analytical results show that CLMAC protocol reduces routing overhead of the sensor nodes in wireless sensor networks.