In an attempt to help root out fraud and other criminal activity, the U.S. Citizenship & Immigration Services agency is making surprise visits to companies with H-1B visa holders on the books.
After reports came out that there has been evidence shown of fraudulent use of temporary workers, bad documentation abusing the system and many visa holders not being paid prevailing wages, the Feds are showing up without notice and looking to see that everything is on the up and up.

From a CIO article on the subject (edited):

Recently, the USCIS has begun making "surprise visits" to the U.S. work sites of companies that sponsor H-1B and L-1 visa holders, including some large U.S.-based financial services companies, says Elizabeth Espin Stern, a partner in the Washington, D.C. office of law firm Baker and McKenzie. USCIS assessors come with a checklist of questions designed to confirm the identity of the employer who petitioned for the visa and the visa beneficiary and to verify that both are in compliance with the terms and conditions of the visa...

The objective of the unannounced on-site visits is clear: to detect fraud and abuses of the visa program. A study conducted last year by the Office of Fraud Detection and National Security estimated that 21 percent of H-1B visa petitions violate H-1B program rules. The offenses range from technical violations to outright fraud. The most common violation was not paying a prevailing wage to the H-1B beneficiary.

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The USCIS overseas the H-1B and L-1 visa programs. One question that some attorneys wonder, however, whether surprise visits, random audits and other fraud detection tactics are in the jurisdiction of this agency? From the same article:

USCIS investigation tactics often exceed what is necessary and reasonable to obtain H-1B application verification information, according to Stern (Elizabeth Espin Stern, of law firm Baker and McKenzie). Unlike the Department of Labor, which has the statutory authority to investigate an employer's compliance with visa obligations but rarely conducts audits unless there are complaints, the USCIS has no statutory or regulatory authority to enter the workplace of H-1B and L-1 visa holders. And investigators do not arrive with search warrants or subpoenas, says Stern.

What's more, USCIS has hired contract workers, who complete a USCIS training course, to conduct the site visits. But many of the contractors lack expertise about how companies maintain employment records or demonstrate employment terms, adds Stern.

Evidently, compliance with the program is voluntary, but imagine if an agency of the federal government busted into your workplace without being prepared? It's not hard to imagine your employer feeling a bit compelled or intimidated to hand over information. 

How nutty are the rules for these visas? Well, they can get rather challenging, especially if your company is considering getting rid of these employees as part of layoffs. Take a look at the blog post When H-1B Visa Holders and the Recession Collide.