If IATSE and the AMPTP can not agree terms this week, then a strike will commence from the 18th October, 12:01am (PDT) (5:01am in the UK).

Any productions in the UK that are produced under the Basic Agreement or the Area Standards Agreement Productions will be affected if they have employed US IATSE members. (This generally be anything produced by the large studios) Those IATSE crew members will have to stand down for the duration of the strike. 

This is the most recent issue of the Basic agreement.

And the Area standards agreement.