Washington state legislators will likely be forced to vote on a measure requiring universal background checks for gun sales next year after supporters turned in a first round of signatures to the Secretary of State’s office.

Backers of Initiative 594 delivered 250,401 signatures Wednesday, more than the 246,000 required to place the initiative before legislators but short of the 325,000 signatures the Secretary of State recommends, due to the number of signatures likely to be deemed invalid. Initiative supporters will continue gathering signatures ahead of the Jan. 3 deadline.

The initiative seeks to require a background check on everyone who purchases a firearm in the state, including through private sales and at gun shows. Only antique guns transferred between family members would be exempt.

Washington allows citizens to file two types of initiatives: One puts a matter directly to a vote of the people, while the other puts an issue before the legislature. If the legislature doesn’t vote to pass the measure, it then goes to the next general election ballot. I-594 is the second type.

Supporters said they pursued an initiative to the legislature because groundwork had been laid during this year’s legislative session.

“We started a productive conversation in the legislature this year, and had strong support from the governor, so thought we should give the legislature one more opportunity to pass legislation supported by nearly 80 percent of Washington voters,” said Christian Sinderman, a Seattle political consultant working on the measure.

Legislation to expand background checks failed to pass the state House earlier this year, despite lobbying from former U.S. Rep. Gabrielle Giffords (D-Ariz.) and Gov. Jay Inslee (D). There’s no indication that any legislators have changed their minds, and Sinderman acknowledged the tough path ahead.

“We are realistic that it will be difficult to pass in Olympia, and if we do go to the ballot we’re confident that we can prevail,” he said.

Gun control advocates have tried to advance new rules through the initiative process before, unsuccessfully. In 1997, voters soundly rejected Initiative 676, which would have required trigger locks to be sold with every gun; 71 percent of Washington voters cast ballots against the measure.