Ask someone — like this Amazon reporter — if there’s anything that can slow Amazon down, and you’ll likely hear an answer that revolves around regulatory concerns; the company continues to flex its power at a time when the U.S. president is looking for reasons to make life harder for Jeff Bezos and his company.

But the chance of regulatory action has still seemed largely far-fetched, partly because of current antitrust law and partly because the president’s Amazon criticism has appeared to largely be relegated to angry tweets and not much more. No longer.

On Friday, the Washington Post reported that Trump has, on several occasions, personally lobbied the head of the U.S. Postal Service — U.S. Postmaster General Megan Brennan — to double the rates it charges Amazon and other online retail partners to deliver packages to customer homes. The most recent request reportedly came four months ago.

Such a change could potentially saddle Amazon with billions of dollars of extra costs, but Brennan, according to the Washington Post, has so far rebuffed Trump’s attempts.

Brennan has so far resisted Trump’s demand, explaining in multiple conversations occurring this year and last that these arrangements are bound by contracts and must be reviewed by a regulatory commission, the three people said. She has told the president that the Amazon relationship is beneficial for the Postal Service and gave him a set of slides that showed the variety of companies, in addition to Amazon, that also partner for deliveries.

Among Trump’s many issues with Amazon and Bezos, who owns the Washington Post, is the arrangement with the U.S. Postal Service — one of Amazon’s main partners in delivering orders to customer doors. Trump maintains that the online retailer is getting a sweetheart deal from USPS, worsening the service’s financial problems along the way. He has ordered a review of the USPS by a special task force that would recommend reforms.

Amazon and the Postal Service have countered that the arrangement is a profitable one for the USPS, though the contract between the two parties is not public. A Business Insider report from April also poked holes in a Citigroup study — which Trump has latched onto — that claimed that the USPS was miscalculating costs associated with Amazon deliveries.

There still might not be anything that can slow Amazon down. But it now looks as though Trump is trying harder than we previously knew.

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