The letter reportedly calls on executives to review ethics and transparency at the tech giant.
Here, we address an underlying structural problems: now we do not have the information required to make ethically-informed decisions about our work, our projects, and our employment.
The employees' pushback against the project follows a similar petition in April protesting Project Maven, a Pentagon contract to use artificial intelligence to improve weaponry.
While Google would like to expand its services in China, it is not clear that it would, or could, said Pichai. "I think if we were to do our mission well, I think we have to think seriously about how we do more in China", he added, according to Bloomberg.
It is not the first time Google employees have spoken out against the company's decisions. Dragonfly and Google's return to China raise urgent moral and ethical issues, the substance of which we are discussing elsewhere.
Before the staff meeting, employees called for more "transparency, oversight and accountability" - according to an internal petition.
In April, thousands of staff criticised its work on a USA military programme developing artificial intelligence for drones.
The China petition says employees are concerned Google's ethics principles "are not enough".
"We urgently need more transparency, a seat at the table and a commitment to clear and open processes: Google employees need to know what we're building", the letter, seen by Reuters news agency, reads.
Google, which has never spoken publicly about the plans, declined to comment. It has said in the past that it will not comment on Dragonfly or "speculation about future plans". "He noted the company guards information on some projects where sharing too early can 'cause issues".
Google's search engine is now blocked in China due to tight controls over speech.
Google services, including its search engine, Gmail and Google Drive, are all blocked in China. It left in 2010 over an escalating dispute with regulators that was capped by what security researchers identified as state-sponsored cyber attacks against Google and other large USA firms.
Employees are concerned by agreeing to Chinese censorship it would violate Google's "don't be evil" code of conduct.