Rachael McRae, a fifth-grade teacher in central Illinois, was sitting on the couch the other day with her 4-month-old when she saw the email."He was having a fussy day," she says, "so I was bouncing him in one arm, and started going through my emails on my phone, just to feel like I was getting something done." In her spam folder, she found an email from an organization called My Pay, My Say, urging her to drop her union membership.Last month, the Supreme Court in Janus v. AFCSME dealt a major blow to public sector unions. The court ruled that these unions cannot collect money, known as agency fees, from nonmembers who are covered by collective bargaining agreements.Organizations on both sides across the country sprang into action. The Mackinac Center for Public Policy, based in Michigan, is running My Pay, My Say as a national campaign. The Freedom Foundation, with headquarters in Washington state, is targeting teachers in Oregon, Washington and California with the slogan, Opt Out Today.Other groups targeting teachers and public employees in specific states include: the Commonwealth Foundation, the Yankee Institute for Public Policy, the Center of the American Experiment, the Center for Union Facts and Americans for Prosperity.The outreach tactics include paper mail, phone calls, emails, hotlines, Facebook ads, billboards, TV advertising and even door-to-door canvassing. Organizations are using publicly available email addresses to reach their targets, as well as purchasing mailing lists."The day after the decision was out," says Randi Weingarten, president of the American Federation of Teachers, groups were already "spamming our members and trying to get them to opt out."Her union just wrapped up its national convention, vowing to redouble its commitment to organizing and member outreach, with a pledge to "celebrate the activism and be somber about the challenges ahead." For the unions, the stakes are clear: Experts told NPR the decision could lead to a huge drop in membership and revenue in the 22 states where these fees had been allowed.The groups behind the opt-out campaign, which describe themselves as conservative, libertarian or free-market, share many donors in common, such as the State Policy Network, the Donors' Fund and DonorsTrust. Many of these groups have long opposed not only agency fees, but teachers unions in general, on the grounds that they inhibit education reforms such as vouchers and charter schools.According to an analysis of tax filings by the website Conservative Transparency, the top contributors to the Mackinac Center specifically include the Dick and Betsy DeVos Family Foundation, and the DeVos Urban Leadership Initiative (formerly the Richard and Helen DeVos Foundation). These are the family foundations of the U.S. education secretary, Betsy DeVos, and her husband's parents.DeVos reported resigning her position on the board of directors of her family foundation as of December 2016, before her confirmation as education secretary.Greg McNeilly, a spokesman for DeVos in her nongovernmental capacity, says the DeVos family supports the Mackinac Center and similar organizations "because of their mainstream common commitment to freedom, the most universal civil liberty." The Mackinac Center did not return calls and emails requesting comment.In a series of Supreme Court cases, ending with Janus, litigants backed by conservative groups argued that their First Amendment rights were infringed by unions' political activities."We know there are tens of thousands of educators who chafe under the left-leaning leadership of these unions," says Jami Lund, a senior policy analyst for the Freedom Foundation. "Making sure they know they now have an option will certainly have its effect."Lund says the pitch to teachers is practical, not political: You can save money, perhaps $1,000 a year. "Our main promotional point is: Opt out today."Their Opt Out Today website, like My Pay, My Say, includes a sample form that people can fill out to create an opt-out letter to then send directly to their union. The group says it is also deploying 80 door-to-door canvassers.These groups are casting a wide net, even though a small percentage of people covered by union contracts currently choose to pay agency fees.Lily Eskelsen Garcia, the president of the National Education Association, told NPR these fees were just 3 percent of about a$370 million budget. The NEA is the nation's largest teachers union, with about 3 million members.Lund says his organization estimates that agency fee payers amount to fewer than 2,000 teachers in Washington state, out of a workforce of more than 60,000.It makes sense. Before the Janus decision, teachers and other public employees had the choice of paying perhaps $1,000 in union dues, or $650 in agency fees (the exact amount varies from state to state, but the ratio is similar in most places). So many teachers chose to pay a little more to get the benefits of full union membership.Now, however, those same people, who may be facing stagnating wages, have the option to pay nothing at all, while still being covered by the union bargaining contract.Lund and others are betting that they will choose to save that money.One of the Mackinac Center emails sent to Rachael McRae in Illinois reads, in part: "The U.S. Supreme Court just ruled that all government workers — teachers, state workers, local public employees, police, firefighters and more — now have a real choice when it comes to their unions ..."Whether it's disagreements about politics, concerns about a lack of local representation, problems with union spending, or something else — you now have the right to stop paying for activities you don't support."NPR Ed put a callout on Twitter, and we heard from McRae as well as teachers in Putnam County, N.Y., and Portland, Ore., who received a similar email and a postcard in the mail. None of the three said that they were dropping their membership.Lund says a few thousand people filled out the opt-out form on the organization's website within the first few weeks.But Weingarten, the head of the 1.7-million-member AFT, says union leaders from New York to Los Angeles are reporting that just a handful of people are actually dropping their membership so far. "What we're seeing is that members are sticking with the union and in fact getting more active and really pissed off," she says.For her part, McRae thinks of her union as "like health insurance or car insurance ... like an extra safety net."She says that she can see some people opting out, especially if they disagree with the union on political grounds.McRae, a mother of three, says she pays union dues of $676 per year. She earns $38,000 as a veteran fifth-grade teacher with 10 years experience. "We don't get paid very much." Copyright 2018 NPR. To see more, visit http://www.npr.org/.