Financial firms are resisting European Union regulators' plans to make investors pay for fixed-income market research separately from trades.

Regulators say the research fee is built into the difference between the price at which broker-dealers, such as investment banks, buy and sell securities, known as the bid-ask spread. The banks counter that research is cost-free for clients, so requiring separate payment would lead to extra costs for asset managers without the narrowing of spreads foreseen by the regulators.

“There is currently no pricing mechanism for fixed-income research,” Andrew Bowley, head of market-structure strategy, EMEA, at Nomura Holdings Inc. in London, said in an interview. “The sell-side is not charging; the buy-side is not paying: there is no price,” he said. “We could double or zero out research spend, and the trading spread on fixed-income instruments wouldn't change.”