AFSCME is an Illinois public sector employee union.
Many say this union has too much control of what happens in government in Illinois. Influencing taxation is a big issue that is said they should not have influence over, since they seem to have a stronger voice than regular tax payers. The issue with their influence is that they lean toward more taxation for the benefit of their members, to excesses, over the reasonable taxation of Illinois residents.

 Janus, a public sector employee and union member is tired of his dues going to pay for union issues he disagrees with, especially increases in taxes in Illinois. With the support of Governor Rauner, he sued to keep his job, and not be forced to be a member of the union. His case is currently being considered by the Supreme Court. 

See more in this Chicage Tribune article:

http://www.chicagotribune.com/news/opinion/commentary/ct-perspec-mcqueary-janus-afscme-unions-20180622-story.html