I am a certified real estate appraiser in Illinois , My company was doing 8-10 ordes a day for a large AMC for about 7 months. The relationship was very positvie until 2 weeks ago when they shut us off due to coming in lower than what another appraiser came in at in regards to the estimated value. We have them on tape stating such and stating the brokers within this bank (a very large lender in Illinois) complaining about our appraisals(values) since then they have removed us from the list. My question is do we have a case to sue for damages due to what we believe was undue influence/pressure?

I do not see the undue pressure/influence?
It sounds like they just don't like your company and prefer another company.
You don't have some sort of binding contract?

I see no basis for a suit. They did not use you 8 months ago but then started. Used you for 7 months and feel they can do better with a different appraiser, end of story. You had no contract and were not employed by them so they did not even fire you, just stopped using you.

My understanding is a Lender can decide what appraisers are qualified to be on their AMC "approved" list and modify it at will based on performance and other criteria. There was no "undue" influence with regards to each appraisal you completed... you had no contact or very little contact with the Lender.

The Lender could have and likely decided to quit using your company and informed the AMC because they didn't like your companies work (e.g. they lost business) and dropped you from their "approved" list. This is not undue influence. Undue influence would be if the Lender contacted you directly and asked you to change a "low" appraisal to a higher value.

Very few Lenders ask for "full-blown" 2nd opinions on purchases because most borrowers don't want to pay for them.

In my opinion, it is likely the AMC just stated what they did because it is easier to say the Lender fired you than the truth which is they (the AMC) found another appraisal company that would churn out the needed appraisals for less money and the AMC had the potential to make a bit more themselves.

What I don't clearly understand is why a "full" 2nd appraisal was done on the same property? Usually these are just reviews.

I am not an attorney but it is my belief that a lawsuit would be a waste of your money & time.

Different topic: The "tape" in many jurisdictions is not likely usable in a court of law unless the person on the other end of the tape knew and consented to being recorded.

Good luck!