Workday, which provides cloud-based human resource software, filed for an initial public offering in what could be the largest market debut since Facebook’s botched May launch chilled demand for US IPOs.

Workday, co-founded by ex-PeopleSoft execs David Duffield and Aneel Bhusri, who left the company following its acquisition by Oracle in 2004, confidentially filed for an IPO in July under the Jumpstart Our Business Startups (JOBS) Act.

Pleasanton, Calif.-based Workday, which is said to have plans for an October debut, filed a preliminary prospectus with the Securities and Exchange Commission to raise up to $400 million.

Bloomberg News, citing sources, reported that Workday has signed up a big customer in Google for its online tools to manage employee operations.