Caml Query to find items with different values in two fields?

In a list, I have two managed metadata columns (let's say Tax1 and Tax2).

I'm trying to find all items where values in Tax1 and Tax2 are different.

I'm using this query:

  <Where>
    <Neq>
      <FieldRef ID="{4C17C478-4F90-480C-A0F2-0BFAA215807F}"/>
      <FieldRef ID="{05F9E914-EED5-4E19-9561-CE795AD63158}"/>
    </Neq>
  </Where>
  <OrderBy Override="TRUE">
    <FieldRef Name="ID"/>
  </OrderBy>

However, I get an error:

<nativehr>0x80070057</nativehr><nativestack></nativestack>

How should I fix my query?

As a side note, my query is fired from a PowerShell script.