Improbable CEO Herman Narula has described the recent changes to Unity's terms of service as "insanity", arguing that indie developers will be hit the hardest.
His comments come after Unity changed the wording in its terms of service efficiently blocking the integration of any "managed service running on cloud infrastructure" or binary add-ons such as SDKs.
Speaking with GamesIndustry.biz, Narula said he would "like to believe this is all just a misunderstanding".
Narula added that Unity's decision was unprecedented, and whatever change it intended to implement shouldn't apply to developers who already have products released or currently in development.
"We just want some answers and we think our developers deserve them too... An engine change is death - for an indie developer it's death," he said.
There is currently no indication as to why Unity made the change, and the engine provider has so far been unavailable for comment.
"The only thing I can think of is this is a mistake or an accident," Narula suggested. "That seems possible.... If it really is that Unity has consciously decided to terminate the development of loads of people who've been developing on our product for years, without telling them... that just seems friggin' insane honestly. I don't know who that helps."
"An engine change is death - for an indie developer it's death"
Herman Narula, Improbable
According to a statement released by Improbable, the change came about during open discussions between the two firms on how they could work closer together in future.
Paul Gardner, a partner at media and tech law firm Wiggin, said it illustrates the hazards of building a product or service on another's platform, and that today's fallout was a "surprising and high stakes move by both companies".
"First by Unity in making what does look to be a significant (and in effect retrospective) change - and by Improbable in going very public on this issue," he told us.
Based on the vague wording, it affects any game using cloud-based SDKs developed on Unity and includes currently live games.
"We're really hoping it doesn't come to a live MMO going down because of a user license agreement change... I'm hoping some kind of sanity prevents that from happening," said Narula. "As the letter of the law is written it is kind of immediate."
One such title that could be at risk is Bossa Studio's Worlds Adrift, though currently the game remains online.
Since our conversation with Narula this afternoon, indie developer Spilt Milk Studios took its game Lazerus offline after it was told the access to servers would be revoked. However, in a recent update the studio has restored the game.
"Until either the servers are forced down or we're told to turn them off, we'll keep Lazarus live," it said on Twitter.
GamesIndustry.biz has spoken with several other studios who said it could spell the end for their in-development projects.
"Unity has been my engine of choice for six years now," said independent developer Trond Fasteraune. "By taking away my ability to use SpatialOS in my Unity games I have no other choice than to move to a different game engine or do something else. And I've never used another game engine.
"I've written in a blog post about how I want to design my games and I also want to build a game company around these design principles. Unity is the perfect choice for these kind of games. If this decision by Unity is something they stand behind, then my plans are dead. Gone forever. And that hurts."
"If this decision by Unity is something they stand behind, then my plans are dead. Gone forever. And that hurts"
Trond Fasteraune, independent developer
Jacopo Pietro Gallelli, founder and CEO of Milan-based Dynamight Studios, said he was disappointed with the situation.
"Things have been looking really, really good up until today," he told us.
Dynamite Studio raised over €100,000 on Kickstarter earlier this year for its MMO title, Fractured. However, after more than 18 months in development, all of that work is now at risk.
"A lot of projects already started will suffer, or be forced to shut down," Gallelli added. "If this situation is not resolved, we are at risk of shutting down... We have the finances to go on for a while. It's not about the money we have in the bank account, it's more about [a] long-term decision.
"We have to find a very important amount of capital if we want to go on. We found that amount of capital already, we've used it, and finding it again obviously is not very easy. That's of course what we would try to do first before shutting down. If we didn't manage to do that, we would have to close Fractured."
Waleed Amer, lead developer at augmented and virtual reality studio Arcane Reality also got in touch to share his dismay.
"We woke up to pretty much the worst news regarding our business," he said. "The game we've been developing for more than two years is now in a legal limbo."
GamesIndustry.biz has reached out to Unity for comment on this issue and is awaiting a response.