The percentage of public school teachers who are members of a teachers’ union has declined about nine percent since 2000.

Recently released data from the U.S. Education Department’s 2015-16 National Teacher and Principal Survey shows about 70 percent of public school teachers currently participate in teachers’ unions. The 2011-12 data showed 74 percent of teachers in unions which is also down from 79 percent in 1999-2000.

Education Week provides a graph depicting the decline in union membership:

The data are published as the Supreme Court stands to hear the case of Janus vs. AFSCME, an Illinois lawsuit that challenges a mandate for public employees to pay union “fair-share fees.” The high court deadlocked on a similar case against the California Teachers Association after the death of Justice Antonin Scalia.

The Sacramento Bee reports California unions fear even greater decline in membership should Justice Neil Gorsuch break the tie against the union in the case:

If Gorsuch breaks the tie as expected, public employee unions in California will not be able to count on collecting some form of dues from everyone they represent. Unions that operate in both “right to work” and “fair share” states say the shift could drive down membership by 15 percent to 30 percent.

Many public employees, however, say they do not want to contribute to unions when 99 percent of their donations go to leftwing causes – many affiliated with the Democratic Party, as reported by the Daily Caller News Foundation.

“Yet roughly 40 percent of union households vote Republican in any given election cycle,” states LaborPains.org.

Using data from the U.S. Department of Labor, the Center for Union Facts shows that between 2012 and 2016, about $240 million of union donations went to progressive political groups and about $307 million was given to organizations aligned with the Democratic Party, including Media Matters, the Clinton Foundation, Mi Familia Vota, the National Democratic Club, Progressive Democrats of America, and Planned Parenthood.

“For years, labor unions have hijacked member dues to fund Planned Parenthood, Emily’s List, and other pro-abortion groups,” said Luka Ladan, communications director for the Center for Union Facts. “Yet many union members oppose the abortion lobby. The Employee Rights Act would require union officials to obtain permission before spending dues dollars on left-wing political advocacy.”

Introduced in the House in May, the Employee Rights Act would enable public employees to opt in or out of representation by labor unions. The bill would also require union officials to obtain permission from members before spending dues money on causes.