The Biden administration’s order to federal workers to get vaccinated against the coronavirus has raised a ticklish question: does it apply to the quasi-governmental U.S. Postal Service?

It’s a big question, because the Post Office has more than 640,000 employees, roughly 200,000 of whom are unionized. But the Post Office is one of those weird hybrids that isn’t entirely federal (it used to be), but not entirely private. So…does the vaccination mandate apply and if so, under what authority?

The answer appears to be “it depends.” Maybe not the order for federal workers. Instead, it could fall under the proposed private employers mandate through OSHA:

“The COVID-19 vaccination requirements included in the White House executive order issued on September 9, 2021 for federal employees do not apply to the Postal Service,” said Dave Partenheimer, a USPS spokesman. “Regarding other vaccination rules expected to be issued by the federal government, the Postal Service has no comment until those rules are issued and we have had a chance to review them.”

Providing testing for unvaccinated employees could prove an onerous task for the Postal Service, which has a workforce spread across 34,000 facilities. USPS was not subject to Biden’s previous mandate for the federal workforce—which required employees to either be vaccinated or receive regular tests—meaning the mailing agency would be starting from scratch in implementing testing infrastructure. Additionally, USPS does not know who among its workforce is already vaccinated.

“We do not track that,” Partenheimer said, adding the Postal Service is encouraging all employees who wish to get vaccinated to do so. In a recent message to employees, postal management told staff that widespread vaccination for COVID-19 is a “critical tool to help stop the spread of the current COVID-19 pandemic.”

The American Postal Workers Union, which represents more than 200,000 USPS employees, previously denounced vaccine mandates and said any issues related to the inoculations or testing must be negotiated with the union.

Whatever the president wants, then, is subject to whatever the union allows. That’s been a big problem for the Postal Service for decade after money-losing decade…never mind the billions in taxpayer-funded bailouts.