XTB sharesfell more than 8% today (Wednesday) to close below 100 zlotys, theWarsaw-listed broker's sharpest single-session decline in months and a strikingreversal of the rally that carried the stock to a record 114 zlotys in April. Tradingvolume ran more than 50% above the three-month daily average, signalinginstitutional positioning rather than retail noise.A Sell-Off Without anObvious CatalystXTB did notpublish an ESPI disclosure on Wednesday. Poland's Financial SupervisionAuthority did not announce a new investigation, sanction, or rule. No analystnote circulated that would account for an 8% repricing of one of the Warsawexchange's best-performing stocks of 2026.Polishfinancial press has connected the slide to renewed unease about the KNF'songoing review of how Contracts for Difference are sold to retail clients. Thatreview, and the regulator's thinking around it, has been public knowledge forweeks.[#highlighted-links#] “Manyinvestors appear to have been spooked by media reports - which, in my view,were somewhat overinterpreted - suggesting that the KNF intends to take atougher stance on CFDs,” Arkadiusz Jóżwiak, the Editor-in-Chief at Comparic.pl,commented for FinanceMagnates.com “The old market adage is to buy the rumor. Thistime, however, we witnessed investors selling it.”As FinanceMagnates.com reported earlier this month, KNFvice-chairman Dariusz Adamski said the "capital market cannot functionlike gambling" and confirmed the regulator was widening its CFD review.What isunclear is why the same regulatory thesis the market discounted two weeks agowould today drive XTB shares more than 8% lower on outsized volume.A Different Reaction FromSix Weeks AgoThecontrast with April makes the move more conspicuous. On April 13, KNF imposed a20 million zloty ($5.5 million) fine on XTB over MiFID II breaches in clientonboarding between 2022 and 2023. The stock rose the following day and keptclimbing, hitting an all-time high of around114 zlotys justover a week later. A confirmed financial penalty did not dent the rally.Six weekslater, with no new fine, no new XTB filing, and no fresh regulator action, thesame stock has given back roughly 11% of its value from the April peak in asingle day. Broader RegulatoryPressure on CFDs Is Building Across EuropeThe Polishregulator is not acting in isolation. The European Securities and MarketsAuthority has spent more than two years tightening supervisory expectationsaround retail leveraged products, and earlier this year acknowledged that MiFID II rules had become too complex for manyordinary investors, while continuing to scrutinize CFD providers' marketing andproduct design.InFebruary, ESMA also confirmed that perpetual futures meeting the CFD definition fallunder the same retail restrictions as traditional CFDs, closing a workaroundseveral crypto-linked brokers had been testing.Spain'sCNMV imposed sweeping curbs on CFD advertising in 2023, and Cyprus's CySEC hastightened oversight of retail-facing client acquisition for the same products.Within thatlandscape, KNF has emerged as one of the more active CFD supervisors in the EU.Its widened review puts the Polish market on a similar trajectory to thegradual tightening seen in France, Spain, and the Netherlands over the pastseveral years.CFDs Still Power aBusiness That Sells Stocks and ETFsThe reasonregulatory chatter, even without a fresh development, can move XTB shares thismuch is the broker's revenue mix. Although XTB markets equities,exchange-traded funds, and investor education to Polish retail clientsalongside its CFD offering, leveraged contracts remain by far the largestprofit driver.Arnaout hasacknowledged this directly, telling Polish media that "around 95%, ormaybe even more, of revenue is generated from CFD instruments." He hasframed diversification, including spot crypto and options, as a multi-yearproject rather than a near-term offset.Thatdependence is why strong fundamentals failed to cushion Wednesday's reaction.XTB's first-quarter 2026 results showed net profit of 535million zlotys, up 176% year over year, on operating income of 1.09 billionzlotys and 370,000 new clients added in a single quarter. NobleSecurities analysts have flagged a full-year 2026 net profit run-rate of around1 billion zlotys, contingent on the broker maintaining current monetizationrates. None of that protected the share price on Wednesday.What Investors Will WatchNextWithout anofficial trigger to anchor the move, the next reference points are external.KNF has not yet published concrete proposals on new leverage caps, marketingrestrictions, or suitability-test changes, nor a timeline for publicconsultation. Whether anyfuture measures will apply only to Poland or extend to XTB's FCA-regulated andCySEC-regulated units is also unclear. Sell-side analysts covering the brokermay issue revision notes in the coming days as they recalibrate regulatory riskinto existing models targeting abillion-zloty annual profit.For now thestock trades roughly 22% above its 52-week low of 61.86 zlotys but about 11%below the April record, leaving room for further repricing if the regulatoryoutlook hardens or if whatever drove Wednesday's volume returns.This article was written by Damian Chmiel at www.financemagnates.com.