UBS Group AG is offering to buy Credit Suisse Group AG for as much as $1 billion, a deal that the troubled Swiss firm is pushing back on with backing from its biggest shareholder.

Credit Suisse, which ended Friday with a market value of about 7.4 billion francs ($8 billion), believes the offer is too low and would hurt shareholders and employees who have deferred stock, according to people with knowledge of the matter.

The UBS offer was communicated on Sunday with a price of 0.25 francs a share to be paid in stock. UBS also insisted on a material adverse change that voids the deal if its credit default spreads jump by 100 basis points or more, the Financial Times reported. Credit Suisse closed down 8 per cent to 1.86 francs at the close on Friday.

Swiss authorities are seeking to broker a deal that would address a rout in Credit Suisse that sent shock waves across the global financial system over the past week when panicked investors dumped its shares and bonds following the collapse of several smaller US lenders.

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A liquidity backstop by the Swiss central bank briefly arrested the declines, but the market drama carries the risk that clients or counterparties would continue fleeing, with potential ramifications for the broader industry.

The complex discussions over what would be the first combination of two global systemically important banks since the financial crisis have seen Swiss and US authorities weigh in, according to people with knowledge of the matter.

Talks accelerated Saturday, with all sides pushing for a solution that can be executed quickly after a week that saw clients pull money and counterparties step back from some dealings with Credit Suisse.

Also read: Indian banks resilient to absorb potential liquidity impact from Credit Suisse stress