The email sent by Schumacher to all practice staff on 29 November 2016 – but recently leaked to the Architects' Journal – states the letter disowning the principal's vision for an entirely deregulated city was never approved.
It claims the letter was sent out by head of press Roger Howie despite being rebuked by all of the company's directors.
Writing from Hong Kong just before midnight via his iPhone, Schumacher accused Howie of signalling "a rift inside ZHA, a rift which does not exist at all", and attempted to reassure staff that it would all blow over.
"Don't worry, I am in charge and won't let you down," reads the email, which is published in full below.
"Roger unfortunately temporarily drowned in the quicksands of the media spin and issued a statement on behalf of ZHA which had nobody's endorsement except his very own," it continues.
"I guess he got carried away by his own virtuoso rhetorical flourish – fighting one front without noticing that he was opening thereby another; he failed to reflect that his punchy phrases could never have been endorsed by me."
Schumacher made the comments during a keynote speech at the World Architecture Festival in Berlin, which was live-streamed by Dezeen and can be watched here in full
The speech – which was first reported by Dezeen and broadcast live on our Facebook page – covered eight demands, which included privatising public spaces, scrapping social housing and dropping all building regulations.
The open letter stated that Schumacher's vision "does not reflect Zaha Hadid Architects' past – and will not be our future".
In Schumacher's response, he hit out at the media for creating news "out of thin air", leading to the suggestion that he might lose his job.
"Please be careful and avoid confrontation," he added.
"I am in good spirits, trusting that my faux pas will be forgiven (by you for sure, but also by the world, our colleagues, clients, etc). Hey, shit happens… and lessons are learned! Politics and professional service don't mix."