In this paper we describe a new medium access protocol termed as the modified grouped-tag TDMA protocol (MGTDMA) for networking radio frequency identification tags. It is known that the previously proposed grouped-tag TDMA (GTDMA) protocol performs very well under the conditions of uniform destination distribution and not so well for heterogeneous traffic conditions. The MGTDMA differs from GTDMA in the sense that MGTDMA allows groups experiencing high traffic to steal (cooperatively) from low traffic groups at regular time intervals. Performance of an access scheme is assessed in terms of average packet delay and average energy consumption. Approximate analytical equation for average delay is derived. More accurate estimates for delay are obtained through simulation studies. We compare the performances of MGTDMA, GTDMA, and a pseudo random protocol and show the usefulness of the new scheme.