Let's take a look at what he writes. 

"Every week, about an hour's worth of pay is taken out of my paycheck to cover my mandatory union dues. If you only work 20 hours, since most service industry jobs are part time, dues can be a whole 5 percent of your paycheck..."

While paying dues is part and parcel of being in a Union in most cases the amount you pay is less and can even be far less than the increased wages and other benefits you receive. 

"Basic economics says that setting a price floor on labor will price everyone unable to create $15 in value out of the market, leaving many low-skilled people, especially young workers, unable to find jobs."

History has proven this false.  When the minimum wage has gone up the economy improves because people have more money to spend. 

Continued