They also asked whether "navigators" will have access to confidential tax documents and what steps the Obama administration has taken to protect consumers against potential fraud.
"The unreasonably low standard for becoming a navigator not only undermines the state’s ability to ensure consumers are protected but raises questions about the appropriate use of federal resources and the protection of highly sensitive consumer information," the lawmakers wrote.
Under the Affordable Care Act, "navigators" will help consumers understand their coverage options in the new insurance exchanges.
Some of the counselors are required to be affiliated with nonprofit groups, but none has to be licensed as an insurance agent or broker.
"Navigators" are not permitted to select a plan for their clients and do not determine individuals' eligibility for federal subsidies.
Supporters say the program is necessary to help underserved communities gain access to ObamaCare coverage.
The Health and Human Services Department has set aside $54 million for the effort and says any participants will have to demonstrate expertise in health insurance and take a 20-30 hour online course on ObamaCare.
Thursday's letter was signed by Senate Finance Committee ranking member Orrin Hatch (R-Utah) and Sens. Johnny Isakson (R-Ga.), Tom Coburn (R-Okla.), John Barrasso (R-Wyo.), Pat Roberts (R-Kan.), Mike Enzi (R-Wyo.), Richard Burr (R-N.C.), John Thune (R-S.D.) and John Cornyn (R-Texas).