It's only for contracts started on or after June 1st. If they tried to raise the ETF for all current customers, by law, everybody would be able to get out of their contract. If the terms of a contract are changed after it's signed, you have the right to cancel it without penalty, since it's not what you agreed to.
Things like this happen quite frequently too. A couple years ago I was on Sprint, I needed to close my contract when I was only 8 months in, due to a job that provided a discount to Tmobile customers. Right around this time Sprint had changed some surcharge by 10 cents, and I was able to use that to get out of my contract, free of charge. Although it was 10 cents, it wasn't a fee/rate I agreed to at the initial contract signing. They'll try to put up a fight, but once you say it's materially adverse to you, they'll let you go.
Carriers are raising costs of ETFs simply because these device are expensive, and I wouldn't be surprised if more carriers follow suit. Too many people were opening up lines of service to get the subsidized price of a phone, and then they turn around and cancel the account, pay the ETF, and then sell the device on Ebay for a substantial profit (recouping the $175 and then some). This is why they're doing it. Carriers give you the phone at a low price, and then make back the cost of the phone (and then some) during the 2 years of service. And when you cancel your account early, the $175 you're paying is a mere fraction of the cost of the phone. These new lofty ETFs prevent that. They make sure they get paid for their phone now.
Side note: I will be a Sprint customer again in 2 weeks time.