Yes, and much more recently we had the IRS stifling political groups that oppose the current administration.
But there's a difference between government stifling of speech illegally and government stifling of speech legally. At least with the former there are legal avenues that can be pursued to correct the situation.
There's not much difference to the person being stifled, at least, not initially.
Yes, you can litigate absurdly expensive court battles (assuming the government allows itself to be sued), have your voice silenced for the years and years your case takes to work its way through the courts, and then, assuming you win, finally get to say what you want a whole decade or more after the fact.
Legal avenues are great like that for people that want to delay, distract, and disrupt.
There's not much difference to the person being stifled, at least, not initially.
There's a huge difference between a government being able to send the police in broad daylight to do its bidding and beat you up or jail you for breaking the "subversive speech law" vs having to deal with some bureaucratic agency making you jump through endless hoops trying to get your group's 501c tax status.
That's all before you even think about getting into a courtroom.
But there's a difference between government stifling of speech illegally and government stifling of speech legally. At least with the former there are legal avenues that can be pursued to correct the situation.