Unite has already instigated legal proceedings against BA over staff travel, so I would assume it has already taken advice on this and the publicised strategy has always been to pursue these issues through both litigation and industrial action.
Regardless of whether it is seeking advice about litigation issues or whether any industrial action under the latest ballot is connected to the previous dispute (BA told Unite it thought they were over six months ago) it seems very late in the day to be seeking advice not least when nothing much has changed over the past six months and Unite has two weeks in which to call a strike.