The National Education Association, the largest U.S. labor union, is pushing to make public schools a front-burner domestic issue throughout the 2016 presidential race, union leaders said Wednesday.

“We have 3 million members who want desperately to know what the candidates have to say to really, seriously improve public education,” NEA President Lily Eskelsen García told reporters. “We intend to activate those 3 million members, the parents, even the students.”

The union, which represents one out of every 100 Americans, has begun its presidential endorsement process, the earliest point it has engaged in a presidential campaign cycle, García said.

Although only one candidate, Sen. Ted Cruz (R-Tex.), has declared his intention to run for the White House, the NEA has sent questionnaires to 19 “viable” candidates to begin the vetting process for an endorsement, said Carrie Pugh, the union’s political director.

On Monday, the union held a virtual town hall for more than 4,000 teachers about the presidential campaign, García said, and later this spring, it will train activists from around the country.

The union is also planning to erect billboards at the airports in Des Moines and Manchester, N.H., to remind candidates flying in and out of early primary states about its public schools agenda, she said.

García would not say what the NEA plans to spend on the 2016 campaign. The union gave more than $16 million to candidates in the 2012 election cycle and devoted $7 million to outside spending, according to the Center for Responsive Politics.

Among NEA’s top issues are the use of standardized tests to evaluate teachers and schools and getting adequate resources for an increasing number of needy children in America’s classrooms, García said.

She also said the NEA is interested in hearing from all candidates, even though many Republican presidential hopefuls have repeatedly attacked teachers unions as barriers to quality education.

Jeb Bush, for example, often clashed with teachers unions when he was governor of Florida. He has referred to public school systems as “government-run unionized and politicized monopolies who trap good teachers, administrators and struggling students in a system nobody can escape.”

While voters often place a high priority on education, historically it has not been a top-tier issue during presidential campaigns. Part of this is because public schools are largely a local matter, although the Obama administration has played a larger role than many in shaping public education and issues such as the Common Core State Standards have stoked a loud national debate and gotten the attention of several presidential hopefuls.

In 2008, the Bill and Melinda Gates Foundation and the Broad Foundation spent $25 million on an ill-fated effort known as “Ed in ’08” that tried to make education a top issue for that year’s presidential race. In the end, Bill Gates said the initiative seemed to succeed only at getting candidates to “mouth platitudes” but not seriously engage in policy debate about improving public education.

García said the NEA will have a better result.

“Even though Gates has lots and lots of money, we have something they don’t — 3 million members,” she said. “We’re going to make this 2016 presidential campaign about students, demand that politicians listen and respect the voices of professionals who know the names of students in those schools.”