In EU a vendor can amend a contract but it gives the client the opportunity to breach that contract without consequences.
On a smaller scale it happens on a monthly basis with telecomms - almost never with rates, but they amend privacy policy and stuff - as a customer a change in the contract gives you an opportunity to say you're not accepting new contract, within certain timeframe, and walk away.
I guess this is simmilar - they told them they are changing the contract, and under new circumstances they will have to pay this and that, but they are free to walk away and pay nothing.
Well, you can amend a contract, but you need to send the new conditions, and it gives the other party option of not accepting the new contract, which means either amending party needs to accept continuation under old contract, or dissolution of the contractual relationship with no fees/damages/etc for the party that didn't accept new contract.
The part that I find egregious is that apparently Slack didn't even send a new contract.
On a smaller scale it happens on a monthly basis with telecomms - almost never with rates, but they amend privacy policy and stuff - as a customer a change in the contract gives you an opportunity to say you're not accepting new contract, within certain timeframe, and walk away.
I guess this is simmilar - they told them they are changing the contract, and under new circumstances they will have to pay this and that, but they are free to walk away and pay nothing.
Still a dick move.