What are "agency fees" and "right-to-work"?

In light of the Supreme Court's decision to review the case of Janus v American Federation of State, County, and Municipal Employees a little info about the labor practices in question might be helpful.

U.S. Department of Labor -- glossary:
https://www.dol.gov/general/aboutdol/history/glossary

FAQs on unions:
https://www.workplacefairness.org/labor-unions

Agency fees:
https://en.wikipedia.org/wiki/Agency_shop

Right-to-work laws
https://en.wikipedia.org/wiki/Right-to-work_law

Supreme Court to Review Case that Threatens Public Sector Unions

The Supreme Court has decided to hear a case that challenges the longstanding practice of unions to collect dues from all bargaining unit members regardless of an individual's decision to join or not join the union.  The case was brought to the Court by "right-to-work" advocates.

http://blogs.edweek.org/edweek/school_law/2017/09/us_supreme_court_to_again_take.html

Background information on the meaning of this review:

http://blogs.edweek.org/edweek/teacherbeat/2017/09/a_primer_on_the_supreme_court_case_teachers_unions_fear.html

Background of the case the Court will review:

http://www.chicagotribune.com/news/local/politics/ct-bruce-rauner-illinois-supreme-court-met-0929-20170928-story.html