, the definition of key terms such as "cybersecurity threat information" is dangerously vague, and could allow Internet companies to monitor and read private emails and online messages.

The opponents also contend that the legislation would allow government agencies to use information provided by Internet companies for a variety of reasons. An early version of the bill contained language that would have allowed law enforcement to go after copyright infringers using the data gathered by Internet companies, they noted.

The legislation wouldn't force companies to share threat data with the government; any sharing of information would be voluntary. "We shouldn't have to rely on the promises of companies," not to share data with the government, Reitman said.

"The major concern we have with CISPA is the fact that it is much too broad," said Kendall Burman, senior national security fellow at the CDT.

"It defines the information that private companies can share with the government in an almost unlimited way," Burman said. The information collection and sharing permitted under CISPA would do more to enable surveillance than serve any cybersecurity purpose, she added.