This is section 1312(d)(3)(D) of the Affordable Care Act. The so-called “Grassley Amendment” says that members of Congress and their staff may only get their health insurance through the exchange or on the individual market. No Federal Employees Health Benefit Plan for them!
Republicans would like to use the budget reconciliation process to repeal the Affordable Care Act (ACA). That process allows both houses of Congress to pass legislation with only a simple majority, effectively bypassing the Senate’s filibuster/cloture rules. But, under The "Byrd Rule" (2 U.S.C. § 644), with limited exceptions, Republicans can only repeal those provisions of the ACA that do "not produce a change in outlays or revenues". So, for example, using budget reconciliation, they might be able to repeal the ACA's surtax on high earners, to repeal funding for subsidies for insurance bought on the exchanges, and to repeal tax penalties for the employer and individual mandates.
However, using budget reconciliation, they cannot repeal the Act's requirement that insurance be sold without regard to health (pre-existing conditions) and other ratings, nor can they repeal the requirement that members of Congress and their staff buy their health insurance on the individual market. To change these non-budgetary provisions, they wlll need Democratic support.
Now, everyone in the health insurance industry agrees, and an Urban Institute study has predicted if Republicans repeal the individual/employer mandates without also repealing the ratings restrictions, the individual insurance industry will collapse. Insurance companies will stop selling individual insurance policies (and group policy rates will increase).
Thus members of Congress and their staff, like the rest of us in the individual insurance market, will be unable to purchase health insurance at all unless the Democrats agree to help them pass a special law that allows only them to escape the devastation they will have caused everyone else. We need to call our Republican Congress members and let them know what they’re about to do to themselves and their staff; and we need to call our Democratic Congress members and tell them we are watching, and we do not want them to agree to any special treatment for members of Congress. If they wreck the insurance market, they need to bear the consequences.