Banks and other companies that have seen borrowing costs rise in the past year are about to feel more pressure in a US$1 trillion market for short-term IOUs.

Investors are poised to pull as much as $400 billion from U.S. money-market funds that buy such debt, known as commercial paper, JPMorgan Chase & Co. predicts. The looming exodus, a consequence of steps to make money markets safer after the financial crisis, is set to accelerate before October. That's when Securities and Exchange Commission rules take effect mandating that so-called institutional prime funds, among the main buyers of commercial paper, report prices that fluctuate. Traditionally, those funds have stuck to $1 per share.

Wall Street strategists say investors may already be shifting from prime funds to those focused on government debt, which will keep a fixed share price. The diminished appetite for commercial paper is a potential headache for banks and other issuers, which saw the cost of the IOUs climb to an almost four-year high in recent weeks. The companies use the instruments for everything from loans to payrolls.