UPS and the Teamsters Union reached a tentative agreement late last month, averting a strike.

UPS also has a market cap of 156B$ vs Fedex's 66B$. Both average around 90B$ in revenue. Fedex drivers maker an average of 52k$ a year. Fedex doesn't have any unions.

In summary, it seems that having a union helps workers earn a lot more, but also help the company have significantly better stock market performance.