Is it a requirement to have a separate EIN for a pension trust?

Well, when your plan sponsor undergoes an audit of the company, and the IRS starts asking about all of these undeclared dividends that were actually received by the Trust, I bet you'll wish you had gotten a number for the plan...

No, I don't think it is a requirement. But, it certainly does make more sense to have a trust EIN since the trust is a separate entity and is treated differently for tax purposes. On the other hand, Ann 84-40 blesses the use of the employer EIN for the tax forms connected with plan distributions. The IRS wants consistency, so you may not want to try to change practice in mid-stream if this is an established plan. Maybe others have had bad experiences as mwyatt has alluded to, but I have not so far. I always get a trust EIN for new plans, but for takeovers where they have been consistently using their employer EIN I let it be.