The story was reported by the Washington Post and Billboard -- with the former citing sources familiar with the situation ... and the latter getting one of the venue's main overseers on record. The VP of ASM Global -- the company that manages the BOK Center in downtown Tulsa -- told the magazine that Trump's campaign had, in fact, given the order.

The VP, Doug Thornton, says the campaign instructed them to stop labeling every other seat with "Do Not Sit Here, Please!" stickers, which the arena staff had already done to nearly every row. The place sits 19,000 -- so, at least 9,500 were presumably used.

There was even video captured and posted by WaPo that shows a few men with badges going around and actually removing those stickers. It's shot from a distance, so it's hard to make out what the stickers say, but it seems pretty clear they were the ones in question.

It's unclear if these guys are Trump staffers or arena staffers. In any case, it's a smoking gun.

This is insane, considering the BOK Center was actually trying to do the right thing and take safety precautions ... only to be thwarted by the man's own team come showtime.

Of course, if you saw the rally live -- not to mention the people lining up to get in before doors opened -- you know it was already a 'rona danger zone. Now, the place ended up being mostly empty inside, especially those upper rows. Still, those that were there did pack in like sardines, and now, we appear to know why -- at least partially, anyway.