Whoa, Matt Lauer! The posh town of Southampton has issued a stop-work order on part of the “Today” star’s sprawling, 40-acre horse farm, reports The Post’s Jennifer Gould Keil. The order was posted late last month on a former office structure that Lauer is turning into a swank residence for up to six groomsmen. Lauer can’t put a home on the property but he can build structures necessary for agricultural-related business, which in his case is an uber-luxurious horse farm. A Lauer source explained, “When tearing down the old office they found rot. We need to fix the roof before work can begin again.” Lauer’s construction team filed the new papers within days of receiving the stop-work order. His massive estate includes 36 horse stalls, a riding arena and a man-made pond where children skated this winter. “We’re not at odds with the town,” the Lauer source added.