There are a number of proposals for technical changes to Bitcoin that may take effect in the coming weeks, so we are taking this opportunity to communicate our plans for managing any resulting network disruption. We take no position on the desirability of any particular proposal nor do we have a stake in any outcome. Our primary concern is protecting our users and their tokens.
As we have done in the past when faced with similar circumstances (1), any decision we make will be with the security of users' tokens in mind. We will be disabling deposits and withdrawals of Bitcoin (and all BTC related tokens) any time we deem necessary to ensure that all tokens stored on Poloniex remain safe. The length of any possible downtime is unknown as this is highly dependent on network stability. Our objective will be to bring the wallet back online and enable deposits and withdrawals as soon as we believe it is safe to do so. Trading will be unaffected during these periods.
At this time, we cannot commit to supporting any specific blockchain that may emerge if there is a blockchain split. Even if two viable blockchains emerge, we may or may not support both and will make such a decision only after we are satisfied that we can safely support either blockchain in an enterprise environment. If we decide to support and make available derivative blockchain tokens after a blockchain split, note that if you have your tokens on loan at the time of a split, we cannot distribute the derivative tokens to you, the lender, as you would not possess them. Such loaned tokens can, and often do, leave the platform. (2)
If you don't want to leave the decision of which Bitcoin tokens to support (or recognize as valid) to a 3rd party, you should not keep your tokens on any 3rd party platform. We encourage you to follow our Twitter and Notices board for updates.
From Poloniex Team