Washington ? Legislation that protects gun manufacturers and distributors against lawsuits over gun crimes passed its first Senate test Wednesday. But Democrats said the cost to Republicans would be public votes on extending the assault weapons ban and requiring comprehensive background checks at gun shows.

The bill providing immunity from suits won the support of 75 senators in a test vote, and opponents acknowledged it has the backing to pass when they get to the final vote on Tuesday. Still, several Democrats and Republicans plan to force votes on less popular gun measures.

“We all know this underlying bill has legs. That’s why we want to get some amendments on there,” said Sen. Barbara Boxer, D-Calif.

Democrats on Tuesday will force votes on a plan that deals with gun shows, where unlicensed sellers do not have to check buyers’ backgrounds. They also want to extend for 10 more years the ban on assault weapons, which expires in September.

“If we can’t amend this bill to add the assault weapons ban, we’re not going to have another vehicle this year,” said Sen. Charles Schumer, D-N.Y.

But the bill’s Republican supporters insist that any attempt to make changes would simply amount to an attempt to kill the bill. For example, the GOP-controlled House already has said it does not plan to approve an extension of the assault weapons ban.

The White House, which has indicated support for the assault weapons ban and the gun show measure, called on the Senate to pass the legislation without amendments.

“Any amendment that would delay enactment of the bill beyond this year is unacceptable,” according to a White House statement.