ObamaCare critics are increasingly concerned with the hub, which will verify applicants' personal information by connecting the new insurance marketplaces with federal agencies.
In one case, the system might tell applicants whether they are eligible for a tax subsidy by using their Social Security number to check their income with the Internal Revenue Service.
In another, it might check individuals' citizenship. Illegal immigrants are not eligible for benefits under healthcare reform.
The lawmakers asked for a briefing from the Health and Human Services Department no later than July 12.