Absolutely MUST be mandatory.
It is voluntary now and there are still millions of illegal aliens working illegally.
Coordinated enforcement across all levels of government as it happens in most other countries is how we reduce illegal aliens.
In Japan if you are overdue to leave by 12 hours, they will find you and deport you.
Whether E-Verify is mandatory or voluntary is still pretty mudy.
HOWEVER-—YOU MUST USE the I-9 form when hiring an employee. There are various kinds of certified papers you can present to get past the I-9. I used to be a payroll supervisor& I had plenty of problems with ranch managers across 7 states following the correct paperwork. I finally demanded a copy of the I-9, a copy of the soc sec card- and other copies for the master files in the headquarters. Funny how compliance was spotty and then they got the message-—I was more stubborn than they were. I got the paperwork I wanted for the master files.