In addition, Fitch places UBS on rating watch negative due to uncertain implications of the acquisition on the combined credit profile of the two banks.
The Treasury Secretary's comments come amid heightened worries about financial stability after the collapse of two US banks and UBS' deal to buy troubled Swiss rival Credit Suisse.
The measure would have rescinded the DOL rule allowing retirement plans to consider environmental, social and governance issues in their investment decisions.
The regulator said that it's seen 'substantial interest' from multiple potential buyers.
The rating agency lowered the bank's long-term issuer credit rating to B+ from BB+, having already downgraded the lender to junk last Wednesday.
The Swiss bank is reportedly paying more than $2 billion for its rival in an all-share deal priced at a fraction of Credit Suisse's close on Friday.
Silicon Valley Bank's parent company filed for Chapter 11 after the bank was placed in FDIC receivership last week.
The plan, which the banks devised with US regulators, is meant to stave off a widening panic in the wake of regulators' seizure of Silicon Valley Bank and Signature Bank over the past week.
JPMorgan, Citigroup and Bank of America are among the big banks that are part of the discussion. Details of the rescue may be announced as soon as Thursday.
Several large banks are discussing a potential deal that could include a sizable capital infusion to shore up troubled First Republic.
