Close one corp, open another, use same EIN?

That chart involves an acquisition and an F reorg. within that acquisition, plus it involves an S corp. OP's does not involve either.

But anyway, I ask the same question as dellpaul. Doesn't matter much who forms the new MT corp., as long as all that happens is a transfer of the assets and liabilities from the CA to the MT corp. as part of an F reorg. That's what's described in 368(a)(1)(F).

Also see post #10 for suggested reading, which is still suggested.

Doesn't an F reorg always require a second corporate entity?

The chart is silent regarding any acquisition. S-Corp/C-Corp/Disregarded Entity... The result is the same. New Co owns Target. MT Corp owns CA Corp

The question is: Does the newly formed MT Corp take over CA Corp's EIN?

And the answer appears to be: Yes

So...We form MT Corp. Don't apply for an EIN for this new corp. Do the F reorg. Start using CA Corp's EIN for the MT Corp. Close CA Corp.

If you keep the same EIN, would the one tax filing reflect both CA and MT activities or would you file a final year / initial year Fed tax return differentiating CA and MT?

One filing.

I am pretty sure this is a no-no.

Client has a CA C-Corp that has been operating for many years. They moved out of CA and have been operating in MT for several years. They have recently set up a new corporation in MT using the exact same name in that new corporation. They want to close the CA C-Corp and just continue operating as before but now under this new MT corp.

What is the harm in them using the old corp's EIN in the new corp?

Don't have a cite, but form experience had CA corps merge out to a different state and keep the same FEIN.
If your client didn't merge out, but opened a new corp in MT, then a new FEIN would be needed.
They can still sell the stock of MT corp to CA corp and merge out to MT with the existing FEIN.
I would get a business attorney involved in this. This should be a relatively simple transaction with a reasonable attorney fee if the goal is to keep the old FEIN.