IOWA CITY  Organizers behind a petition drive seeking to overturn Iowa Citys 21-only bar law believe they have enough signatures to send the matter to voters.

George Wittgraf, owner of the Union Bar, and Josh Erceg, a manager at Martinis, another downtown bar, submitted the petition to the city this month. It calls for a referendum that would repeal the city ordinance that bans people younger than 21 from being in places with liquor licenses after 10 p.m., with limited exceptions.

They got 5,716 people to sign the petition. They need the signatures of 2,500 registered Iowa City voters to force the City Council to either adopt the proposal or to send it to a public vote. The timing of the referendum would put it on the November ballot if it is deemed valid.

Wittgraf said Friday that at least 80 percent of the people who signed the petition are college students. While that raises the question of how many of them are registered to vote in Iowa City, he said hes confident theyll meet the 2,500-signature requirement.

He said it was not hard to get students to support an effort that would allow 19- and 20-year-olds in bars at night.

Especially the younger kids, once we told them what it was for, they were all about it, he said. Right now, theyre stuck leaving (bars) at 10.

Just three years ago, the student vote was not enough to overturn 21-only. After the council adopted the law in spring 2010, voters upheld it by a margin of 52 percent to 48 percent that fall.

One line of thinking has been that once the law was on the books and students, and residents elsewhere in the community, get used to it, it would be hard to defeat it.

Outgoing University of Iowa Student Government President Nic Pottebaum told The Gazette in May, after Wittgraf and Erceg gave notice of their petition drive, that there had been a huge cultural change downtown as far as the students go and he did not hear much about a wanting to return to 19-and-older bars

Mayor Matt Hayek said in an email the petition puts three years of progress on alcohol-related issues at risk.

"I think the community has less of an appetite to revisit the issue than it did in 2010," he wrote. "I think people recognize 21-only is working. And some of the leading pro-19 advocates from 2010 support keeping 21-only in place."

That includes some downtown bar owners and student leaders.

The City Clerks Office has until July 1 to certify the petition and expects to be finished by the end of next week. City Clerk Marian Karr said her staff will do much of the work comparing the signers to the voter rolls next week.

Hayek said he believes the City Council would have zero interest in repealing the 21-only law, so with a valid petition, the proposal likely would go before voters.

A November vote would be the third time in six years the issue has been on the ballot, with each side claiming one victory so far. Before the 2010 election, voters failed to approve a 21-only law in 2007.

Wittgraf said a rubber match this fall would be decided by student turnout at the polls.If the students want it, they need to get out and vote, and it should be pretty easily won, I think, he said.