Before we waste dozens of posts while WT chases another "sliver of exclusivity," let's all make sure we're clear on what's being discussed. For the sake of this discussion, and context (and at the risk of being seeing as talking down):
Pension: A defined benefit (DB plan) that is paid at retirement. The monthly amount is usually defined by a negotiated multiplier based on years of service. That cannot be unilaterally changed out side of negotiations, nor can the amount-per-hour a company agrees to pay in for a multi-payer plan (like the IAMNPF). As WT notes, how a company (or IAM) funds the plan can be changed w/o labor's say, as long as the above covenants are still met.
401k: A defined contribution (DC plan) that is self funded, and generally tapped into at retirement. A company contribution separate from what an employee may pay in and a set percentage of matching funds (usually either dollar-for-dollar or 50%)up to a set amount may also be involved. As noted earlier, DL pays in 2% regardless of employee participation, and will match dollar-for-dollar (100%) up to another 5% of whatever an employee kicks in. In a CBA, those factors cannot be changed outside of negotiations. Obviously, the vagaries of the market cannot be controlled by either party, either. A company may change the fund options that are that are available to invest in unless otherwise negotiated.
PMNW employees (depending on hire date) currently have a frozen pension from NW, one that is in a sort of limbo from the IAMNPF, and a 401k. If you had a 401k at NW, it was transferred over from ING to Fidelity, and the respective fund options "mirrored" as best as possible until you had a chance to go in and tweak it to your liking.
At any rate, relevant to this thread, DL can do whatever they want, whenever they want. For example, a large portion of the plan options we have available to invest in were simply created out of thin air. No track record to research, no nothing. Tey can also alter the parameters of our plan at will. As Yoyo notes, it's pretty "sweet" right now, but that doesn't mean it will always be going forward...