Part of the push on this issue comes from the number of visa petitions that are being rejected. From 2005 through 2007, the denial rate for L-1B petitions ranged from 6% to 7%; in 2008 it rose to 22%, and has not sunk below that level since; in 2011 it was at 27%, according to Bo Cooper, an immigration attorney at Berry Appleman & Leiden. He testified in February at a U.S. House hearing on immigration policy.

According to U.S. State Department data, the U.S. received just over 91,000 L-1 visa applications in 2010. It received about 71,000 petitions in 2009, and 97,000 in 2008.

In 2008, the USCIS, coincidentally, also produced a study showing that one in five H-1B visas are affected by either fraud or "technical violations." Although this study was focused on the H-1B program, Grassley and Durbin have made changes to the L-1 visa part of their reform effort. Among the changes they have sought for the L-1 visa is imposing a prevailing wage requirement on these workers, as well as preventing the "outplacement" of L-1 visa holders to other firms.

The issue being raised in both the White House letter and the Grassley and Durbin letter concerns the interpretation of "specialized knowledge," a requirement that's applied to the L-1B visa. An employee who gets an L-1B must have knowledge that "is beyond the ordinary and not commonplace within the industry.... In other words, the employee must be more than simply skilled or familiar with the employer's interests," according to USCIS.

The signers of the White House letter argue that U.S. immigration authorities have adopted an "inconsistent and improperly narrowed definition" of specialized knowledge. The USCIS is now reviewing the guidance it gives to adjudicators.