Q:

Correct use of "Call for Proposals" in plural context

I'm trying to correctly refer to several calls. Meaning, in a singular call, we invite several proposals. Therefore, it's a call for proposals.
In the case I need assistance with, my gut tells me when referring to past calls that have gone out, I should refer to these as, calls for proposals. At them moment, my colleague has stated several calls as call for proposals. For example, "View Our Past Call for Proposals."

A:

I believe that is incorrect. A single call is calling for multiple proposals for addressing a single task, hence "A call for proposals". If there are multiple tasks, you emit multiple calls, each asking for multiple proposals. Those are correctly called "calls for proposals". 
e.g. "These are all the calls for proposals we have published for construction, renovations and repairs on this campus."

