Regulators have raised competition concerns over a Scotland-based financial technology firm's takeover of an Australian rival.
FNZ, which is based in Edinburgh, acquired financial software company GBST in November in a deal which valued the Australian firm at at £152m.
But the Competition and Markets Authority (CMA) said it was concerned that the merger could result in UK investors losing out as a result of higher prices, fewer options and less innovation.
Both firms provide software to retail investment platforms in the UK.
In a statement, the CMA said its initial investigation had found that FNZ and GBST were "close competitors in what is a concentrated market with few other significant suppliers".
It added: "Smaller or less well-established firms find it difficult to enter or scale up because of the risks and reluctance of customers to change suppliers."
Joel Bamford, senior director of mergers at the CMA, said: "Investment software is critical to the operation of retail investment platforms which are used by many investors in the UK.
"FNZ is already the largest supplier and has purchased an established rival who is trusted by many platforms, with few remaining competitors left in the market.
"We are therefore concerned that this transaction could lead to customers losing out."
FNZ has been given five working days by the CMA to address its concerns. If it fails to do so, the deal will be referred for an in-depth investigation.
FNZ said: "FNZ looks forward to continuing to work with the CMA to address their concerns."