From the letter:

[A]fter last week's hearing, it is obvious that there are multiple issues that need to be reviewed and discussed before the Committee is prepared to mark up the bill.

We believe that more hearings are necessary to adequately address a number of important issues with broad implications for our economy. Specifically, we believe that the issue of mandatory apportionment of damages, post-grant opposition, and broad rulemaking authority for USPTO need to be more carefully examined to ensure that they do not undermine innovation, increase frivolous litigation, or undermine property rights. Many prominent American businesses on the cutting edge of innovation are expressing concerns about the impact of sweeping patent reform. These concerns merit thoughtful deliberation.

Consider the Patent Reform Act of 2007 derailed.