How can I preserve the source MAC address on a gateway machine before forwarding data it through another eth.

For example I have eth1 and eth2 both belong to different networks. If some data is coming on eth1 on a particular port, by using IPTABLES I am forwarding it to other network through eth2. Before going out of the system packet has the source IP and source MAC of eth2. I want to have only source IP of eth2 but source MAC to be preserved as earlier.

Is it possible to do by adding some rules in iptables POSTROUTING chain ?