What are the pros and cons of well compensated STEM graduate students joining a union? Recently, my state has declared graduate students as employees giving them the right to unionize. The students in the Engineering School are very well compensated. The benefits that we get are


Minimum stipend of 29k$ (which was increased ~3 years ago). 
Top tier health insurance plan fully paid for by the University and Engineering School
Deans that largely respect student needs and actively address current issues
Plethora of funding for student lead activities 
Free services like legal council, psychiatrist, campus clinique, campus shuttle buses, etc.
TA opportunities are always available for those that need them. 


Additionally, my department has a very high standard set forth for us. We have nice offices, the Chair actively addresses our concerns and complaints, funds for student activities and community building, computational resources, and more. The quality of life for students in my department (Applied Math) is quite high. 

Lately, we've had outside people dropping by to advise us to join a union. The humanities students are largely in support of this movement since they are not compensated as well as the engineering students. In my point of view, there are very few reasons why I can see joining a union will benefit the Applied Math graduate students. Given how well we, the graduate students in my department, are currently treated, what are the advantages and disadvantages of unionization? 

Edit: There is a similar question here, however, does not specifically address STEM students. 

I am a naive graduate student and will like to be better informed about the advantages and repercussions of joining a union. Whenever administrative University personnel have approached us to dissuade the effort, their tone has been extremely diplomatic and ambiguous about why they are advising against unionizing.

A brief summary of the responses is as follows.


Advantages of unionizing


Security of current benefits
Bargaining power to timely address current, new, and growing needs of the entire bargaining unit 
Guaranteed minimum pay 
Improving circumstances of students in other schools who are not as well compensated
Human resources like representation for students facing abuse, harassment, or other adversities from their advisors

Disadvantages of unionizing 


Partisan representation 
Clarifying the distinction between student and employee (though some may argue that this is an advantage)
Paying dues (though contracts usually negotiate higher stipends to offset this amount)
Deterioration of student/administrative relationship



Additional STEM specific points that I'd like to add are


Advantages


Incentives to address issues such as a single student having to monitor experiments running for 8+ hours
For international students, alleviating fears of not being able to find an advisor which prevents them for settling to the 1st person that says yes regardless of their interest 
Some departments in the Engineering school offer things like funds for all students in their 3rd year to purchase a new laptop. Adapting this or similar policies universally would be appreciated.
Guaranteed funding beyond X years as set forth by the School, especially when the average is just slightly below X. 

Disadvantages 


As funds are rerouted into increased stipends, there may be 


Decreased support for professional development (conferences, workshops, etc.)
Decreased supplemental resources (rented compute nodes and hours, new lab equipment, etc.)
Fewer graduate student and postdoc hires




Thank you all for your comments; it is all very much insightful. I'll continue to look out for new responses.
The Fair Labor Standards Act (FLSA) of 2016 set a minimum salary of $47,476 for professional employees to be exempt from paid overtime. in response to this, the NIH changed its postdoctoral salaries.

While the NIH says


  NIH is fully supportive of increased pay for postdoctoral researchers and has proposed to increase the NRSA postdoctoral stipends to levels above the threshold


their behavior suggests otherwise. What they did is simple increase all postdoctoral salaries below the minimum to slightly higher than the minimum. While historically a year 1 post doc made 4% more than a year 0 postdoc, after the adjustment they made the same. There was no increase in the predoctoral salaries. In FY 2016 the NIH predoctoral salary was $23,376 so slightly less than what you are currently being paid. 

While you may believe you are well compensated, some would argue that $29,000 a year is not a fair salary if you are expected to perform unpaid overtime (and what graduate student doesn't work overtime). A union can help fight for things like fair salaries.