The White House’s deep involvement in hiring decisions across the government is frustrating some of President Donald Trump’s Cabinet secretaries, spurring early tussles between the president’s advisers and leaders of federal agencies.

White House officials have sometimes rejected candidates who have previously criticized the president — even if they boast sterling credentials or have the endorsement of top Republicans. And they’ve often imposed their choices on agencies, according to more than a dozen people inside and close to the administration.

Many Cabinet nominees joined the administration believing they’d have wide latitude to pick lieutenants, but they’re beginning to realize Trump’s powerful advisers are looking over their shoulders. The White House’s approach has already slowed hiring — and the dozens of vacancies at key agencies could make it more difficult to implement some of Trump’s policy proposals.

So far, Trump has nominated fewer than three dozen of the 550 most important Senate-confirmed jobs, according to an analysis by the Partnership for Public Service, a nonprofit group that advised Trump officials during the presidential transition.