The nation’s business and lobbying interests began publicly mobilizing Tuesday in a coordinated attack against House Democrats’ signature campaign finance, lobbying, ethics and voting overhaul, which the full chamber plans to vote on Friday morning.

More than 300 groups including the U.S. Chamber of Commerce — the top spending organization on federal lobbying — and numerous other state, federal and conservative-leaning organizations wrote to lawmakers attacking the bill for “pushing certain voices, representing large segments of the electorate and our economy, out of the political process altogether.”

The letter came days after one of the bill’s chief foes, Senate Majority Leader Mitch McConnell, who has crusaded against the measure, urged outside allies in a Capitol Hill meeting to heighten their opposition — even though the Kentucky Republican has already said he will not bring the measure for a vote in his chamber.

And the White House, adding more weight to the onslaught, issued a veto threat — even though McConnell pledged to block even a vote on the measure. The White House Statement of Administration Policy objected to the bill on several grounds including this one: “H.R. 1 would prohibit commonsense efforts to clean up voting-rolls to limit opportunities for voting fraud. The bill would also require States to adopt online registration, same-day registration, and automatic voter registration, thus imposing a one-size-fits-all standard for weighing the competing values of voter access and voting integrity.”

The vote in the House this week is widely considered the opening act in what may become a multiyear debate and a major messaging point in the 2020 presidential and congressional campaigns. Opponents of the measure say they’re taking this fight seriously because if Democrats win control of the Senate and White House, the ideas behind HR 1 would likely be a top order of business.