Final answer:
The NFL union differs from the MLB mainly because the NFL has a salary cap, limiting the amount of money teams can spend on player salaries, thus promoting parity. MLB lacks this kind of cap.
Step-by-step explanation:
To answer how the NFL union is different than the MLB, we look at various aspects of their collective bargaining agreements and how they relate to players' salaries and benefits. The NFL union does have differences in comparison with the MLB. Most notably, the NFL has a salary cap, which is a limit on the amount of money a team can spend on player salaries. This is contrasted with MLB, which does not have a salary cap, basically allowing teams to spend freely on players, although there are luxury taxes that come into play in MLB when payrolls exceed a certain threshold. The existence of a salary cap tends to lead to more parity between teams in the NFL, as wealthy teams cannot simply outspend others to acquire all the top talent.