WASHINGTON — Two top Senate Democrats are calling on financial regulators to examine the role of financial technology firms and how their activities interact with the existing regulatory structure.

In a letter to the Federal Reserve, Office of the Comptroller of the Currency, National Credit Union Administration, Federal Deposit Insurance Corp. and Consumer Financial Protection Bureau, Sens. Sherrod Brown, D-Ohio, and Jeff Merkley, D-Ore., said it is critical that fintech firms be subject to rules similar to those that long-standing financial services firms face.

"As we think about the role of fintech, we must be mindful that some of these products, activities and business models may be new and innovative, while others may largely resemble those of existing, federally regulated firms," the letter said. "These companies are changing financial services, and it is vital that the regulators and Congress understand all the impacts and take actions as appropriate."

Brown, the top Democrat on the Senate Banking Committee, and Merkley, the ranking member of the panel's Financial Institutions and Consumer Protection subcommitee, specifically sought details on fintech business models, the regulatory oversight of third-party service providers and protections for consumers and small businesses.

Among the activities outlined as of particular interest were marketplace lending, consumer lending, alternative payments, crowdsourcing, personal finance management, virtual currencies, blockchain and distributed ledger, as well as "your views on the impact of these firms on the institutions you regulate."

The letter also highlights the relationships that federally insured depository institutions have with nonbank technology firms that originate loans. Recent tumult in the industry — most notably at Lending Club, whose chief executive resigned earlier this year after some third-party investors said they would no longer purchase its loans — has made the relationships between the firms and third parties all the more pertinent, the letter said.

"Recent event raise questions about the relationship between regulators, financial institutions and third-party service providers, specifically the policies and internal controls put in place to address possible risks associated with certain lending practices and transactions with financial institutions," the letter said.

Regulators have increasingly turned their attention to the role that technology is playing in driving innovation in the financial services industry, with Comptroller of the Currency Thomas Curry saying last month that the office was examining whether it has the statutory authority to offer a limited charter to technology firms. The Treasury Department and CFPB have also taken steps to examine the issue.

But the senators' letter suggests that Congress might be gearing up for a more coordinated examination of fintech companies. Earlier this month the House Financial Services Committee held a hearing on the role of fintech companies in the financial sector.