House GOP conference Chairwoman Elise Stefanik of New York said in a statement she also plans to vote against the bill, meaning the top 3 members of House Republican leadership are all united in opposing the legislation.

House GOP leaders also plan to formally whip against the Senate's bipartisan gun bill, according to Republican sources.

A formal whip notice is expected to go out on Wednesday.

But even with House GOP leaders opposing the bill, there are already some Republican members who have indicated they plan to vote for it, and the Democrat-controlled House is expected to be able to pass the legislation once it passes in the Senate.

The Senate appears to be on track to pass the measure as early as this week.

The bill includes millions of dollars for mental health, school safety, crisis intervention programs and incentives for states to include juvenile records in the National Instant Criminal Background Check system.

It also makes significant changes to the process when someone ages 18 to 21 goes to buy a firearm and closes the so-called boyfriend loophole, a major victory for Democrats, who had fought for a decade for that.

In contrast to the decision by the top 3 House Republican leaders to oppose the bill, Senate Minority Leader Mitch McConnell has said he plans to support it.

McConnell praised the bipartisan gun violence legislation on Wednesday as a "package of commonsense and popular solutions to make these horrific incidents less likely" that will not "touch the rights of the overwhelming majority of American gun owners who are law-abiding citizens of sound mind."

He said past attempts to pass legislation to curb mass shootings at schools and elsewhere stalled because Democrats tried to "roll back" people's Second Amendment rights.