I'm a software developer working at a company with several clients.
Part of my job is to stay in touch with clients and make sure the software I'm developing for them fulfills their needs. Additionally, I'm the go-to guy for documentation, issues, technical discussion, future development, etc.
Over the years I've naturally developed more than software: a reputation with people (some in far away places), which I could describe as both professional and friendly. They are often project managers or middle management.
If I quit my current job can I ethically ask these clients for letters of recommendation?