The coalition is called Reform Government Surveillance (RGS). From the letter, posted yesterday on the RGS Tumblr page:

Any mandatory decryption requirement, such as that included in the discussion draft of the bill that you authored, will to lead to unintended consequences. The effect of such a requirement will force companies to prioritize government access over other considerations, including digital security. As a result, when designing products or services, technology companies could be forced to make decisions that would create opportunities for exploitation by bad actors seeking to harm our customers and whom we all want to stop. The bill would force those providing digital communication and storage to ensure that digital data can be obtained in “intelligible” form by the government, pursuant to a court order. This mandate would mean that when a company or user has decided to use some encryption technologies, those technologies will have to be built to allow some third party to potentially have access. This access could, in turn, be exploited by bad actors.

Read the whole letter here.