Yes, but I am more skilled than my colleagues.
Unions inherently negotiate on behalf of the median worker who was employed at the time that the contract negotiations took place. As other people have pointed out, the fact the unions negotiate for current employees rather than future employees contributes to the "screw the new guy" phenomenon; the fact that unions negotiate for the median worker can result in them undervaluing their high-productivity workers.
This is why unions are effective primarily in low-standard-deviation-productivity fields: If the best secretary in the office is 10% more productive than the median, but the union manages to raise the median secretary's income by 20% compared to the market clearing rate, then every secretary benefits. However, if the top software developer is 10x as productive as the median...