What will give employers disincentive to hire illegals is a comprehensive immigration policy.
My blueprint:
1. Step up fines/penalities for knowingly illegally hiring an illegal and make this painful enough to be a real disincentive.
2. Put a comprehensive guest workers program into place that can be utilized by employers who first make a good faith effort to hire Americans and, if there are no takers, can import a work crew for that job only. Guest workers will be screened and furnished with ID with a fairly short term expiration date at which time they are required to renew it if the job is still in progress or return home. Overstaying the invite is grounds for immediate deporation and denial of permission to return to work.
3. Employers do not necessarily have to provide it but will be responsible to be sure their guest workers have adequate food, housing, healthcare and, when the job is ended, transportation back to their home country.
4. Employers will pay guest workers the prevailing wage for their area less reasonable deductions for food, housing, and healthcare if that is provided by the employer.
5. The Guest workers cannot bring non-working members of their family with them under this program.
6. Positive photo ID will be required in order to receive a guest worker permit or use whatever reasonable means is necessary for authorities to be able to identify and recognize the worker at any time.
7. Institute a 30 to 90 day period of 'no fault/no questions asked' during which illegals can make necessary arrangements and return home to apply to return under the guest worker program. (Local private charities will probably step up to help pay travel expenses to those who must have it, but most travel back and forth to their home countries on a regular basis anyway and this really would not be a hardship. It is a way to make the illegal legal without providing amnesty, however.)
8. Guest workers who come into the country legally can get on the list for consideration of green card status or citizenship if they want that. Those who do not comply with the law will, when they are caught, be photographed, DNA samples taken, and as much I.D. collected on them as possible and then they will deported and subject to arrest if they return illegally. Such people will be on a list of 'undesirables' and will not be eligible for green card status or citizenship.
9. The Constitution will be amended so that children born to U.S. citizens will receive automatic U.S. citizenship but not those children born to non citizen moms who happen to legally or illegally be in this country when they give birth.
10. Employers are responsible to report to ICE or whomever that a job has ended and the workers will be given a reasonable period (say 3 days) to return home. Employers will be responsible to be sure the workers have transportation to get home.