In an open letter to U.S. Senators a powerful coalition of technology companies including Google, Apple, Facebook and others called for passage of the USA FREEDOM Act surveillance reform package as Sen. Harry Reid scheduled a vote to advance the measure Tuesday.

“The Senate has the opportunity to send a strong message of change to the world and encourage other countries to adopt similar protections,” wrote CEOs of the companies comprising the Reform Government Surveillance coalition. The CEOs called the bill “bipartisan” and said it “protects national security and reaffirms America’s commitment to the freedoms we all cherish.” Signatories to the letter include Facebook’s Mark Zuckerberg, Apple’s Tim Cook, Google’s Larry Page, Microsoft’s Satya Nadella, Twitter’s Dick Costolo and others.

The USA FREEDOM Act is a package of changes to the way the U.S. National Security Agency conducts mass surveillance of American citizens chiefly sponsored by Judiciary Committee chair Sen. Patrick Leahy (D—VT). Debate over the issue accelerated a year and a half ago after leaks from former NSA contractor Edward Snowden revealed vast non-public surveillance programs and duplicity on the part of some officials about the extent of the programs.

U.S. Senate Majority Leader Harry Reid (D—Nevada) called for a cloture vote on Tuesday to end debate. Cloture requires a 60-vote majority is likely to be the biggest hurdle the legislation would face on its path out of Congress.

Though major interest groups, including the American Civil Liberties Union, the Electronic Frontier Foundation and the President’s own surveillance reform task force have backed the compromise legislation passage is anything but certain. Intelligence Committee chair Sen. Dianne Feinstein (D—CA) is reported to have reservations about the bill and other surveillance hawks have expressed outright hostility toward the measure. On the other side of the issue, libertarian-leaning Sen. Rand Paul has said he will oppose the bill for not going far enough to rein the NSA.

In current form the bill puts new limits on the NSA’s ability legally to gather up bulk U.S. phone meta-data and installs special privacy advocates in the Foreign Intelligence Surveillance Court, the body that oversees and authorizes NSA activities. The measure also forbids the NSA from storing data it collects in its own computers, instead requiring telecom companies to retain the data for up to five years. Some critics say the measure puts onerous restrictions on the NSA’s ability to protect Americans from harm. Others say the bill actually codifies and formalizes surveillance practices that once existed in a legal grey area.

“This is a first step in surveillance reform. This is by no means the whole kit and caboodle,” Director of the ACLU’s Washington Legislative Office Laura Murphy tells TIME. “For over the last decade we’ve been empowering government with more and more capabilities to surveil with less and less protections for its citizens. This legisaition would mark a departure from the trajectory since 9-11. We think it’s a very important first step.”

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