CSL Ltd (ASX: CSL) shares are in the red today.
Shares in the S&P/ASX 200 Index (ASX: XJO) biotech stock closed on Friday trading for $299.79. In morning trade on Monday, shares are swapping hands for $296.90, down 1%.
For some context, the ASX 200 is also down 1% at this same time.
Despite that dip, that still sees the stock up 28% since 30 October.
And it makes CSL the third largest company listed on the ASX, with a market cap just shy of $145 billion.
But it's not the big surge in CSL shares that's brought the biotechnology giant under regulatory scrutiny in the United Kingdom. Or, at least, not directly.
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What's happening with CSL shares in the UK?
As you may be aware, CSL's three operating segments are CSL Behring, CSL Vifor, and its Seqirus businesses.
CSL Vifor is a global leader in iron deficiency and iron deficiency anaemia therapies. The company acquired Vifor Pharma for US$11.7 billion in 2022 in a deal that boosted CSL shares once completed.
At its capital markets day presentation in October management noted, "CSL Vifor will continue to grow its leading iron franchise through market expansion and life cycle management."
CSL's iron-deficiency treatment is known as Ferinject.
But in possible headwinds for CSL shares, Vifor has run into a potentially sticky patch in the UK, where some four million people suffer from iron deficiency anaemia.
As Reuters reports, the UK's Competition and Markets Authority (CMA) launched an investigation last Wednesday into whether Vifor Pharma disparaged a competing iron-deficiency treatment produced by its competitor Pharmacosmos to benefit Ferinject.
CMA will investigate whether the company impinged on Pharmacosmo's business by making misleading claims to medical professionals about the safety and efficacy of Monofer, Pharmacosmos's competing treatment.
CSL has not yet responded to the allegations.
But if the CMA finds the company did engage in anti-competitive practices, CSL shares could come under pressure amid a potentially sizeable fine and the accompanying reputational damage.
