Sen. Ron Johnson (R-Wis.) said Thursday that the Washington, D.C., health board has taken the healthcare mandate in the Affordable Care Act too far.

In a letter to D.C. Mayor Vincent Gray, Johnson asks the mayor and the D.C. Health Benefit Exchange Authority (HBX) Executive Board to explain its decision to require all D.C. small businesses to purchase healthcare through exchanges created under the Affordable Care Act.

Johnson argues the decision would prevent people in the District from keeping their current doctors and health plans.

“This decision pushes far beyond any other implementation of the law,” Johnson said in a statement Thursday. “Contrary to promises made by President Obama and reiterated by [Health and Human Services] Secretary [Kathleen] Sebelius that the American public can keep their current doctors and insurance plans, this decision denies those in the District that very freedom.”

D.C.’s exchange board approved a plan earlier this month that would require small businesses (those with fewer than 50 employees) and people who purchase insurance on their own, rather than through an employer, to buy their coverage through the exchange.