Thousands of teachers rally to demand higher pay and increased education spending in Raleigh, N.C., on May 16. (Marti Maguire/Reuters)

This spring, teachers have been striking across the country — in North Carolina, Colorado, Kentucky, Arizona, Oklahoma and West Virginia, all states where they’re barred from forming unions. Surprisingly, teachers’ unions, it turns out, don’t increase teacher salaries — something that these teachers are achieving nevertheless.

But teachers’ unions do accomplish something politically notable: They are a vital part of liberal coalitions and the Democratic Party. Teachers’ union organization and mobilization, like that of other government workers’ unions, have long compensated for the declining membership in traditional organized labor. What’s more, they’ve advanced the causes of women’s and LGBTQ rights — rights that are important to many or most of their members. They’ve done that by delivering money, mobilization and organization to both the Democratic Party and to feminist groups.

Since the 1970s, teachers’ unions have become more important to the Democratic Party

When preexisting networks of people who’ve come together for nonpolitical causes — say, unions, churches or hunters — turn to politics, they can be especially effective at influencing parties and public policy. When they’re invested in a party’s future, they help build bridges and manage tensions among other groups in the coalition. And that benefits both the parties and the organizations: Without coalitions, factions pursuing particular policies often fail.

As traditional unions lost members in the 1970s, teachers’ unions increasingly assumed some of this responsibility. They are particularly influential, given that teachers are not only numerous but also distributed in every congressional district in America.

My ongoing research into the archives of the National Education Association (NEA) and American Federation of Teachers (AFT) shows that both organizations became far more potent in politics as their members turned to collective bargaining. NEA created a national PAC in the 1972 that quickly became a player in Democratic Party politics. A party consultant for the Kennedy and Humphrey campaigns advised the NEA that the PAC “has it within its power to become the single most influential force in American politics,” specifically mentioning that it could surpass the AFL-CIO, “the undisputed leader,” in three years.

By the 1976 Democratic Convention, the number of NEA and AFT delegates rivaled those from all other unions together. By the 2012 convention, as Jonathan Ladd notes, teachers’ union members made up 16 percent of all delegates.

Further, since 1990, the AFT has been one of the top 10 contributors to federal campaigns in five election cycles, and NEA has been one of the top five contributors in seven. In state politics, political scientists Michael Hartney and Patrick Flavin argue that when states adopted collective bargaining for teachers in the 1960s and 1970s, that significantly increased teachers’ political participation.

Why teachers’ unions fight for cultural liberalism

Because teachers’ unions are disproportionately female, they have been particularly alert to gender discrimination. At conventions, union leaders argued that the lack of well-paying opportunities for women in other professions reduced both male and female teacher salaries. As a result, teachers’ unions have advocated for such efforts as passage of the Equal Rights Amendment (ERA) and robust equal pay laws.

Public school teachers have also opposed the same culturally conservative groups that oppose feminist group agendas. For instance, antiabortion groups like Moral Majority supported laws that would enable families to use vouchers and tuition tax credits to send their children to religious schools, which would take that money away from public schools. And so teachers’ unions joined with other opponents of cultural conservatives — and in many cases incorporated their issues as well.

From early on, the NEA aimed to lead the liberal coalition

As I learned in my archival research, the NEA PAC in particular planned not just to advocate liberal policies but also to help meld liberal interest groups into a coherent coalition. A research firm advised early on that “in ten years, the NEA should be in a position where it has strong alliances with other groups in which it plays a leading if not a dominant, but certainly not a subservient, role.” The NEA leaped on that suggestion. It capitalized on contemporary opposition to newly elected President Ronald Reagan to rally feminist, gay rights and liberal groups. Executive Director Don Cameron wrote to his colleagues:

A score of new coalitions will emerge and most will seek heavy support from NEA. The disarmament groups will likely flounder from their incapacity to harmonize disparate views. Americans for Democratic Action will seek leadership status but won’t be able to get it together. … Nevertheless, all of these will likely remain useful to NEA and its interests.

For example, NEA headquarters offered ERAmerica free office space and staff assistance. NEA also hosted meetings of NOW, the NAACP, Lambda Legal Defense and Education Fund  and like-minded groups to oppose the Family Protection Act of 1981, which would have disallowed federal legal aid for abortion, divorce and gay rights.

According to in-house surveys, rank-and-file teachers would have preferred to see their unions focused more narrowly on education policies and teacher benefits. That’s a perennial divide among many groups’ membership and leadership, as passing most policies requires coalition efforts. But few teachers asked for refunds for the portion of their dues spent on PAC money, and teachers’ conventions were effective at raising voluntary PAC contributions.

The political effects of weakened teachers’ unions

Teachers’ unions remain important to party politics and liberal coalitions into the 21st century. For example, Rhode Island teachers and the UAW helped LGBT rights forces pass a marriage equality law in 2013 by giving the liberal advocacy group Ocean State Action both funding and office space for that effort.

And when public-sector unions lose power, so do liberal and Democratic causes. Consider the fact that after Wisconsin passed laws restricting public-sector unions’ power in 2011, teachers’ union membership dropped 30 percent — and membership dues dropped by 50 percent. As a result, teachers’ unions have smaller preexisting networks to mobilize on behalf of political causes.

Of course, both conservative and liberal groups and politicians know this, which is why one side fights to weaken public-sector unions — and the other side fights to preserve them. And it means that if the recent teachers’ mobilizations become drives to unionize, that may well affect the political character of their states.

Chris Baylor is an American Political Science Association congressional fellow and author of “First to the Party: The Group Origins of Political Transformation