Can iptables manager source mac address?

[NetSnake <netsnake@xxxxxxx>]

  I use iptables to nat to internet, but I found some user use a proxy
on intranet, like, 192.168.0.5 can access to internet, 192.168.0.10 can
not access to internet, now 10 access a proxy on 192.168.0.5, then he
can access now, I thought in package from 192.168.0.5 must contant some
information about proxy, like source mac address, this can help me to
identified users, can iptables do this?

  Thanks.