TL;DR: This looks like a highly localized usage, so localized that there is virtually no direct evidence of it available. The term is occasionally used with the straightforward meaning "at the option of the business in question (rather than mandated by some other party)," often enough that there are at least a few examples available. Possibly the more idiomatic meaning grew out of this usage.
It sounds like your informant was using the term something like
That is, business in scare quotes to show that optional really isn't. With this meaning, I would expect usage to look something like this:
Yeah, the holiday office party is optional—"business" optional. Last year, Fred didn't go. Oh, you don't know Fred? That's right, you started right after the New Year.
However, the only use I have been able to find evidence for of the phrase "business optional" is to mean that something is at the discretion of the business, rather than some other party. For example:
even if a bar fails to display the 51% sign as they should, it is you the CHL holder who has the responsibility of not going. Unlike 30.06, which is business optional, actual bars are an auto no-go for CHL holders. Always check the liquor license on their wall. (User comment to "CC Question!!", TexasCHLforum, August 18, 2011)
This one was from a discussion about Texas "concealed carry" (of firearms) regulations in restaurants/bars; essentially, this person is saying that concealed weapons are automatically banned by the state from "actual bars", but restaurants (which get less than "51%" of their income from liquor) can ban them (by displaying a "30.06" notice) or not, at the business's option (rather than mandated by the government).1
Business Optional Time of Use for Northern Service Territory
If your business operations allow you to shift your on-peak usage to mid-peak or off-peak hours, you may want to take advantage of our optional Time of Use (TOU) rates. (Nevada Energy informational webpage)
Here, the issue is whether the timing of a business's peak energy consumption are at the business's option or mandated by its business model/customer needs.
Microsoft automatically updates consumer PCs (and Office 365), but that doesn't work in larger enterprises, which need to ensure apps are compatible. The change is likely to be to a two-tiered cadence: consumers are continually updated, but enterprise users have a stable "long term servicing" release which only sees urgent security patches, with other updates rolled in at a more leisurely pace. "Consumers will continue to be given monthly updates, but these may be business-optional," Silver said. (Angus Kidman, "When Windows 10 will be released (And how to plan for it)", LifeHacker, Nov. 21, 2014)
And here, immediate installation of Microsoft updates is optional for businesses, but still mandated by Microsoft for individual consumers.
It also looks to me like this is the way the phrase is being used in the Guardian article DavePhD linked in a comment to his answer, though that example comes the closest to the usage under discussion as it seems to contrast "at the option of the business (RyanAir)" with either "mandated by the government" or, most tellingly, "at the option of the customer" (that latter interpretation is very similar to "at the option of the business, rather than the employee".
These uses are fairly rare, and the references aren't from the Northeast US, but I'd say that this straightforward interpretation of the term ("business optional" = "at the option of the business") is probably at least as common as the meaning "optional, but there will be CONSEQUENCES should you fail to take us up on the option".
Edited to add:
On further consideration, I think it is plausible that the wink-wink, nudge-nudge meaning developed out of the literal meaning. Folks familiar with the phrase meaning "at the option of the business, rather than mandated by someone else" could transfer it to a situation where it means "at the option of the business, rather than at the option of the employee." I would still use the phrase with caution, and a heavy dose of non-verbal cues to get your point across.
1 Text of Texas Texas Penal Code § 30.06 here, if anyone's interested.