This isn’t good. While we don’t know exactly how many illegal aliens pay taxes for certain, the ones who were looking to legalize their status are motivated to obtain tax ID numbers and pay because the government considers evidence of tax filings when weighing their cases. This is not a rare situation; it is more or less expected of illegals who submit applications to resolve their status that they have a few years of tax returns. Going forward, illegal aliens will be disincentivized to file taxes. Depending how this information is used, it effectively punishes the illegal aliens who did the right thing and rewards those who didn’t.
This exchange of information alone will not motivate illegal aliens to leave, so people who would otherwise be paying taxes while using government services will continue to use them but will stop paying into them.