The Health and Human Services (HHS) Department said the report was false, citing final regulations that mandate "up to 30 hours of training" for the workers.
"The training requirements and elements for navigators have not changed," said HHS spokeswoman Joanne Peters.
"The time it takes for an individual to complete the training program will vary, but will be a minimum of 20 hours as an initial base training, with periodic refresher trainings, the total of which will result in up to 30 hours of training, consistent with the final rule."
The "navigator" program is designed to help people shop for insurance on the new marketplaces, though they will not directly enroll applicants.
Black's letter requested background on the training program and asked if the healthcare industry was consulted on decisions about the hours required.
—This post was changed to reflect HHS's comments on the Wall Street Journal report.