More than 400 Google employees have signed an open letter urging Google to cancel an in-development Chinese search app, on the grounds that it will enable censorship and human rights violations by the Chinese government. The letter was published yesterday with 11 signatories; as of this afternoon, it has 407, most of which are from software engineers. It follows an internal letter circulated earlier this year, which garnered 1,400 signatures.

The letter opposes Project Dragonfly, a China-focused version of Google search that would reportedly block certain search terms and make it easy for the government to surveil users’ searches. Google has repeatedly declined comment on Dragonfly, saying that its work is “exploratory” and that it is “not close to launching a search product in China.”

Dragonfly has drawn criticism from outside Google; among others, Vice President Mike Pence condemned it last month. It’s also garnered opposition internally, among employees who say Google executives have ignored their concerns. “Our opposition to Dragonfly is not about China: we object to technologies that aid the powerful in oppressing the vulnerable, wherever they may be,” the letter says. “Dragonfly in China would establish a dangerous precedent at a volatile political moment, one that would make it harder for Google to deny other countries similar concessions.”