Check out the companies making headlines before the market's opening bell.

First Republic — The bank tumbled about 19% premarket after Standard & Poor's cut its credit rating again, to B+ from BB+, on Sunday. S&P first lowered First Republic's credit rating to junk status last week. The rating remains on CreditWatch Negative.

UBS, Credit Suisse — Shares of UBS fell about 5% before the U.S. open, while Credit Suisse shares plunged 58%. UBS announced Sunday it would buy Credit Suisse for 3 billion Swiss francs, or $3.2 billion, as part of a deal orchestrated by Swiss regulators and the Swiss central bank. Other European banking stocks were also lower, with Deutsche Bank down 1.8% and ING Groep off by 4.2%. 

New York Community Bancorp – New York Community Bancorp jumped 25% in early trading after the Federal Deposit Insurance Corporation announced over the weekend that the bank's subsidiary, Flagstar Bank, will take over large parts of Signature Bank's deposits and loan portfolios, and all 40 of its branches.

Enphase Energy — The battery storage stock added 1% after Raymond James upgraded it to outperform from market perform, noting the selloff in Enphase shares, which are down nearly 31% this year.

US Bancorp — Shares of the bank holding company gained more than 4% in early trading, paring some of last week's 19% loss following the closures Silicon Valley Bank and Signature Bank. Some analysts said UBS's forced Credit Suisse merger over the weekend could boost investor sentiment toward U.S. regionals.

PacWest, Zions, KeyCorp — Shares of other U.S. regional banks were mostly higher early Monday morning as investors appraised the likelihood of expanded deposit insurance. Shares of PacWest rebounded nearly 20% premarket. Zions Bancorp. and KeyCorp each added about 2%.

— CNBC's Sarah Min, Michelle Fox Theobald, Jesse Pound, Tanaya Macheel contributed reporting.