How do you say "constancia de trabajo" in English?
An example: "Necesito una constancia de trabajo para pedir un préstamo en el banco"
I don't think that Joey is talking about steady employment at all. He means a piece of paper, a certificate, that states that he is currently employed somewhere.
Constancia de Trabajo - "Letter of Employment"
If you haven't been regularly employed (if you have long gaps between positions) or if you haven't worked anywhere for a long duration, then they may turn you down for the bank loan.
Welcome to the forum!
It could be "permanent employment", for official use, or "full time employment."
"Steady job" is a less formal way of saying it.
I agree with Gekko re the piece of paper theory. I have seen "una constancia" a couple of times or four used to mean a certificate or a formal letter although I can't now remember any details.
On second thoughts, I believe I needed one when the Argentine police lost my identity although what exactly it said escapes me.