[ornitorrincos]

When companies are so big that operate in multitude of markets, yes, and depending on how many and the size of those disapproving the merger gets cancelled or parts of the business split, accommodations for those disapproving and so on.

Which is why such mergers take a long time.

Now, being both based in the US, the US could say no and it would not happen and no need for any other regulator to consider the merger.