If (and it is a very big if) BASSA are intent on damaging BA's revenue by threatening strike action they need to be very careful. Unless they have a genuine grievance they might fall foul of TULRCA. BA could then sue for loss of revenue. Sure, there's a soundbite in it for the union, but the cost will be severe. I quote from the act
Liability of trade unions in proceedings in tort
20 Liability of trade union in certain proceedings in tort
(1) Where proceedings in tort are brought against a trade union—
(a) on the ground that an act—
(i) induces another person to break a contract or interferes or induces another person to interfere with its performance, or
(ii) consists in threatening that a contract (whether one to which the union is a party or not) will be broken or its performance interfered with, or that the union will induce another person to break a contract or interfere with its performance, or
(b) in respect of an agreement or combination by two or more persons to do or to procure the doing of an act which, if it were done without any such agreement or combination, would be actionable in tort on such a ground,
then, for the purpose of determining in those proceedings whether the union is liable in respect of the act in question, that act shall be taken to have been done by the union if, but only if, it is to be taken to have been authorised or endorsed by the trade union in accordance with the following provisions.
(2) An act shall be taken to have been authorised or endorsed by a trade union if it was done, or was authorised or endorsed—
(a) by any person empowered by the rules to do, authorise or endorse acts of the kind in question, or
(b) by the principal executive committee or the president or general secretary, or
(c) by any other committee of the union or any other official of the union (whether employed by it or not).
Thus threatening strike action without a ballot could be a tort.
Legal bits aside, I predict that certain parts of the media will talk of this as a mass meeting even though the largest room at the venue is barely able to hold 750 people. It would be a body blow to BASSA if they were unable to fill that with supporters given that four times that number rejected the pay deal offered. Of course it won't be representative of the rank and file, only a naive fool would believe that to be possible. The whole meeting is a bit of a gamble in some respects. If there is a small number who are prepared to challenge the BASSA hard line in the meeting, it could backfire badly on the union. Instead of headlines about possible strikes, the media may talk of internal union strife and the way that dissent is handled by BASSA.