What's the need for a new plan? Congress already has a plan in place, it's called employer sanctions. The problem is they're not being enforced.
Part of the PLAN which recognizes the wider scope of the problem:
Under my (Bush's) proposal...Employers must not hire undocumented aliens or temporary workers whose legal status has expired. They must report to the government the temporary workers they hire, and who leave their employ, so that we can keep track of people in the program, and better enforce immigration laws. There must be strong workplace enforcement with tough penalties for anyone, for any employer violating these laws.