Amazon (AMZN) and other companies have been fighting price gouging on their platforms as coronavirus fears prompt nervous consumers to hoard supplies to deal with possible quarantines and related disruptions.

It’s just one of the problems online platforms that involve third-party sales face: Amazon barred a million products because they falsely claimed they could do something to defend against the coronavirus, which has caused 3,214 deaths so far, according to Johns Hopkins’ aggregator.

Amazon’s public line on price gouging has been: “there’s no place for price-gouging on Amazon.” And the retailer has been coronavirus-conscious, especially in Washington, one of the first states to see coronavirus activity. (Already, an Amazon employee has tested positive and the company is preparing itself for remote work for some of its employees.)

But still, prices for some goods have skyrocketed. While Amazon may have surge restrictions in place for its own products, third-party sellers offered — and in some cases still offer — cheap products at wild prices after Amazon’s own stock was exhausted.

Sen. Ed Markey (D-Mass.) sent a letter to Amazon Wednesday telling the company that “corporate America has a responsibility to prevent profiteering on the sales of items such as hand-sanitizer and surgical masks,” and gave the company until March 18th to respond.

View photos HONG KONG, CHINA - 2020/02/12: A man wearing a face mask holds a box of the American electronic commerce company Amazon in Central district, Hong Kong. The death toll from the covid-19 coronavirus epidemic passed 1, 100 and infected over 45, 000 people worldwide on February 12. (Photo by Miguel Candela/SOPA Images/LightRocket via Getty Images) More

Cursory checks of the website Wednesday afternoon showed prices for a pack of eight one-ounce Purell bottles for $89.99. It usually costs around $13 on Amazon. This has been the case for many other products, like N95 masks and disinfecting wipes.

Lysol disinfecting wipes (a package of four containers) averaged $11.79 from Amazon before they sold out, according to Camel Camel Camel, a popular Amazon price tracker. After Amazon’s own warehouses ran out, prices spiked among third-party sellers to almost $180 before coming down to $54.

Amazon, to its credit, had kept prices stable until supplies ran out. (See where the green line turns to dots.)

View photos Products like disinfecting wipes have spiked. Here's the price history from the past month via Camel Camel Camel. (screenshot via Yahoo Finance) More

A 3M high-efficiency dust mask 20-pack cost $19 on Amazon until the end of January. It then spiked to $70, and then went up to $144. Amazon has been cracking down on third-party merchants that have been listing products for exorbitant prices, so there’s typically only a handful of “offers” at a time at a particular price. (Dust masks are not thought of as effective against viruses.)

View photos 3M N95 masks prices have fluctuated wildly after Amazon sold out of them. (Camel Camel Camel via Yahoo Finance screenshot) More

Looking at the price history for a more effective type of mask — though public health officials are saying masks are not effective and hoarding them is not a good idea — shows Amazon’s behavior more clearly. For an N95 3M respirator, Amazon’s price rose a little with the demand, going from around $15 to $27. That was the price Amazon itself — not third-party sellers — charged for their last mask.

But even though Amazon, the price for these masks went up to $249. As Amazon purged these listings, prices fell and went back up as new sellers, looking to take advantage, stepped in.