I’m not sure when the original law was passed, but it was reaffirmed by SCOTUS in 2012. Prohibited by the FEC:
>Making any contribution or donation of money or other thing of value, or making any expenditure, independent expenditure, or disbursement in connection with any federal, state or local election in the United States;
There’s more, but the above covers a good chunk of it.
[0] https://thecaucus.blogs.nytimes.com/2012/01/09/supreme-court...