From this:

About 1,000 employers nationwide will be audited for possible immigration violations in an escalation of the Obama administration's effort to increase pressure on business owners not to hire illegal immigrants.

The businesses will get a notice that the government intends to audit their compliance with immigration laws, the Department of Homeland Security said. The sweep follows a similar action in July during which authorities audited 654 employers. Agents will check the eligibility of workers at each firm, with violations potentially leading to fines, as well as civil or criminal charges.

As the article points out, this happens at the same time as the Obama administration is pushing comprehensive immigration reform. To whatever extent this is a crackdown, they're trying to appear that they're doing something in order to make amnesty more likely, just as the Bush administration did.