It's important for us to distinguish between disabling buy/sell services, closing a Coinbase account, and preventing access to funds.
Disabling Buy/Sell Services
From time to time, due to violations of our User Agreement, Coinbase may restrict access to buy/sell services on a customer's account. This can happen for a number of reasons including, but not limited to, high risk of fraud. When this happens, customers retain full use of their digital currency balances even though buy/sell services are disabled. Additionally, any funds remaining in USD, EUR, GBP, CAD, or other local currency balances can be withdrawn to a verified bank account.
Closing a Coinbase Account
Similar to above, due to violations of our User Agreement, Coinbase may initiate closure of customer accounts. This can happen for a number of reasons including, but not limited to, engaging in prohibited activity as defined in our User Agreement. When this happens, buy/sell services are disabled and in addition you are no longer permitted to use your Coinbase account as a digital currency balance. However, you are allowed to withdraw all funds from your Coinbase account and send it to any wallet address you choose, so access to digital currency is never "frozen" in this case. You are also allowed to clear any local currency balances from your account by withdrawing to a verified bank account before the account closure proceeds.
Note that if your account is closed in this manner while a buy or deposit is pending, the funds will be available to withdraw once the transaction completes.
Preventing access to funds
In extremely rare circumstances, and only where required by law, Coinbase may block or "freeze" customer funds on our platform. We will take this action only when:
We are required to comply with an order from a court or other authority that has jurisdiction over Coinbase which compels us to restrict access to funds.
We are required by law to freeze or block assets in compliance with a sanctions program, including, but not limited to sanctions programs administered by the U.S. Office of Foreign Assets Control (OFAC).
Note that some Coinbase products (such as the multisig vault and paper wallet) do not allow Coinbase to control digital currency private keys, and therefore Coinbase cannot prevent access to digital currency stored with these products.
For reference, our Prohibited Businesses and Prohibited Use Policy.