Does changing a UNIQUE KEY lock the table? (no replies)

Hi,
I have a large table with about 4 million rows in it. Usually ALTER TABLE operations take a significant amount of time and lock the table during the process (understandably so).

We need to remove a UNIQUE KEY that we currently have on this table and add a new UNIQUE KEY to replace it.

I have taken a look at the MySQL documentation for ALTER TABLE but I cannot see much mentioned about table locks for UNIQUE KEY. Will this operation cause a table lock?

Kind regards