"upon a request" is correct and usable in written English.
You can use it when you are asking someone for something or referring to a request that has been made. For example, "Upon request, I can provide additional information about the project".
upon a request by any committee of Congress, to that committee.
Waivers under subparagraph (B) may be granted only upon a request submitted by a Service district office to Service headquarters.
The C-USP Subcommittee on Academic Progress may stipulate otherwise by acting upon a request for fewer units (i.e. reduced course load).
Upon a request from the United States, Mexico may either extradite the individual, or submit the case to the proper authorities for prosecution in Mexico.
The court denied Apollo's motion for judgment before trial, finding that Cooper's obligation to provide "reasonable access" was only triggered upon a request for that information by Apollo.
It was unclear how the judge would handle this latest jury missive; upon a request from Mr. Seabrook's lawyers, the parties met in the judge's robing room for a brief discussion, which was not made public.
(b) Upon receiving a request, the INS will determine the victim's immigration status.
But the judge suggested that he would look favorably upon such a request if it were presented by the bureau.
Upon receiving a request, a state transition to "sensing" or "relaying" may occur.
Upon receiving a request, a staff member contacts both the relevant agency and the small business within two days.
Specifically, each node, upon receiving a request of resource reservation, divides the original request into sub-requests addressing this new set of requests to its descendent neighbors.
