In any case, we just sent a request to FREE about their military intentions. This can be useful for us in estimating their intentions of trading us rubber or not. But we should imo still start planning for taking that one tiler in addition to Cattaraugus.
After reading the posts here, I am leaning more towards the opinion that we should not talk to FREE about this first, or ask permission, even if I said that above.
FREE would in any case have a good excuse to serve up to SABER if that is their major concern. They can take that one tiler back, or even SABER could do it, when they fancy it. It would be good for us to make a stab at two sources at the same time. It is more likely to succeed on one of them, although the Native American saying from Civ4 makes be a bit uneasy - "if you chase two rabbits, you will lose them both."
But it is possible that such an act towards that one tiler could severe our "good" relations with FREE, however good they may be IF they get offended by it, cause in my eyes that partially proves that they were not going to trade us rubber anyway, and that they are just stalling on that now. If their intentions are honourable towards us, it is the perfect excuse for them towards SABER.
So...I reckon it is not really in our interests to inform FREE. It is an interesting move that will most probably get them to show their hand.
And additionally, like Paul says, this mission, if successful, could also spark some tension between FREE and SABER...IF they are not already at war...cause then they should be.
All the better on that account too.