Dueling rallies from rival advocacy groups and a new ad from Republican Joe Lhota are once again making charter schools a major issue in the city’s mayoral race.

Families for Excellent Schools, which organizes parents at charter schools, has called a press conference before tonight’s mayoral debate between Lhota and Democrat Bill de Blasio. Organizers said their message will reiterate a call for the next mayor to open 100 new charter schools in his first four years in office.

Around the same time in Brooklyn, New Yorkers for Great Public Schools, a coalition formed to oppose the Bloomberg administration’s education policies during the campaign, will rally outside the Panel for Educational Policy meeting. The panel is expected to approve more than a dozen proposals to expand or open charter schools inside district buildings in 2014 and beyond, long after Mayor Bloomberg has exited office, and the group’s press advisory says the protest will target “Bloomberg’s ‘lame-duck’ proposals” and ”Lhota’s charter-centric message of doubling down on failed and divisive Bloomberg policies.”

The two events come a day after Lhota released a new campaign ad highlighting the stark contrast between his charter school stances and Democrat Bill de Blasio’s.

The ad, titled “Rally,” features scenes and voices from last week’s pro-charter school march across the Brooklyn Bridge. Lhota joined the march, which was meant to send a signal to de Blasio that his plan to charge rent to charter schools has a large swath of potential voters angry. Lhota would continue the Bloomberg administration’s policy of not charging rent to charter schools in public space, and he wants to double the number of charter schools in the city — a pace of growth larger than what Families for Excellent Schools is calling for.

Two marchers featured in Lhota’s ad say de Blasio’s positions on charter schools make him a less attractive candidate to them. But neither says she would vote for him, though.

That jives with what parents at the rally told GothamSchools. Many said that while they disagreed with de Blasio’s charter school positions, they also were reluctant to vote for a Republican, whose positions on other policy issues are unlikely to match their own. Charter school advocates are also increasingly working to influence de Blasio, the solid frontrunner, rather than support Lhota.

Whether the issue will resonate with voters on Election Day next month remains to be seen, but new polling results suggests it won’t. A poll released last week two days after the charter school rally showed de Blasio retained a wide lead over Lhota.