The Act's constitutionality was challenged in 1947 in United Public Workers v. Mitchell, and again in 1973 in United States Civil Service Commission v. National Association of Letter Carriers. In both cases, the Supreme Court decided that although the restrictions imposed by the Act on the free speech of federal employees infringe on their first amendment rights, this infringement is justified in order to maintain the smooth running of government - noting that Congress remained free to restate this balance if it so desired.
In 1947, a 'balancing test', also employed in 1882 in Ex parte Curtis, was used to weigh up "the extent of the guarantees of freedom against a congressional enactment to protect a democratic society against the supposed evil of political partisanship by classified employees of government". Justice Reed, in the majority opinion of the Court, wrote that "The conviction that an actively partisan governmental personnel threatens good administration has deepened since Ex parte Curtis", and that therefore the Hatch Act's infringement of free speech was justified.
In the 1973 case, an injunction was sought against the enforcement of the Act, on the grounds that the appellants' first amendment rights were being violated. The majority opinion rejecting this contained a similar argument - that although the Hatch Act restricts the speech of federal employees, this is necessary to ensure the smooth operation of the Government;
Until now, the judgment of Congress, the Executive, and the country
appears to have been that partisan political activities by federal
employees must be limited if the Government is to operate effectively
and fairly, elections are to play their proper part in representative
government, and employees themselves are to be sufficiently free from
improper influences. E.g., 84 Cong.Rec. 9598, 9603; 86 Cong.Rec. 2360,
2621, 2864, 9376. The restrictions so far imposed on federal employees
are not aimed at particular parties, groups, or points of view, but
apply equally to all partisan activities of the type described. They
discriminate against no racial, ethnic, or religious minorities. Nor
do they seek to control political opinions or beliefs, or to interfere
with or influence anyone's vote at the polls.
The Court's ruling on Pickering v. Board of Education was also mentioned, in which it was found that a balance should be arrived at "between the interests of the [employee], as a citizen, in commenting upon matters of public concern and the interest of the [government], as an employer, in promoting the efficiency of the public services it performs through its employees."
In weighing up this balancing act, the majority opinion, although acknowledging that Congress retains the right to strike a different balance if it so wishes, states:
We think the balance it has so far struck is sustainable by the
obviously important interests sought to be served by the limitations
on partisan political activities now contained in the Hatch Act.