Fire them. And if existing civil service law doesn't allow that, change the law

 Federal "workers" 

Federal "workers" 

The Washington Post reports that federal workers are organizing and being coached by former Obama administration officials to resist the president and his policies. Work slowdowns, sick leaves, and simply refusing to follow orders. This offers a grand opportunity to cleanse the stables, and Trump should take advantage of it. Judging from his performance so far, I'm confident he will.

UPDATE: I needn't have worried, Trump's team has been consulting with Governor Walker on how best to deal with civil service unions.

Wisconsin Gov. Scott Walker said Wednesday that he spoke with Vice President Mike Pence about how the White House can implement on a federal level parts of the Republican governor’s contentious policy that all-but eliminated collective bargaining for public sector unions in the state.
President Donald Trump has talked about wanting to weaken collective bargaining protections for federal employees, most of whom can’t currently bargain over wages or benefits, to make it easier to hire and fire government workers and base pay on merit rather than tenure. Those changes would require an act of Congress.
Walker severely restricted union power in Wisconsin and is now talking with the Trump administration about “how they may take bits and pieces of what we did” with the union law and civil service reform and “apply it at the national level.”