This move comes as a result of widespread dissatisfaction among BECTU members over their levels of pay. No date for such a ballot has been confirmed but it is quite possible that it will be called for some time in March.
Disputes over pay are not rare in any industry, and there are two sides to this particular debate, so there's a good chance that a compromise will be reached before any strike action happens.
A vote for a strike would in any case not mean an immediate and blanket strike over the whole of the West End: once authorized, strike action could be gradual, incremental and selective - if poor pay is the problem then going without pay at all for any length of time would be counter productive to BECTU members as well as detrimental to theatre in general.
—by Paul Webb Theatrenow