If companies are unable to tap credit to pay their rent, make payroll or finance other activities, it could force them to slash costs, lay off workers, pause investments and even declare bankruptcy. That, in turn, could worsen the recession that’s now widely expected and affect the financial markets — already stressed from stock-market plunges — where investors buy and sell the debt issued by companies, making it even harder for companies to borrow.

“The economy is coming to a half of a dead stop,” said Michael Greenberger, a professor at the University of Maryland Francis King Carey School of Law. Businesses are having trouble opening or getting customers to engage normally, said Mr. Greenberger, whose research focuses on financial stability. “All of these businesses are going to at some time have to re-up their loans, renew their loans, roll them over. With the decline in revenues the ability to borrow money is going to be very problematic.”

On Sunday, the Federal Reserve took the drastic step of slashing interest rates to nearly zero and enacted measures to keep credit pumping through the economy and prevent a wave of business defaults and closings. And in a letter to President Trump and congressional leaders on Monday, the United States Chamber of Commerce asked for sweeping changes to laws governing the Fed so that businesses with more than 500 employees could borrow directly from the Fed’s discount window, a lending facility that is open only to banks.

Such measures could ease a potential credit crunch for companies, which rely heavily on borrowing to function. Larger companies often issue bonds to investors or tap credit from banks to fund operations, refinance existing debt, build plants and even buy other companies. When the bonds are sold into the financial markets, credit rating agencies give them a letter grade, which signals their quality. Grades with As are the best. Bonds with B or C grades indicate a higher probability that investors will not recover their value, because the companies that issued them might stop making payments — but they provide better returns.