There is plenty of precedent for the US government issuing national security letters (“NSLs”) containing gag orders for ongoing investigations, often with massive monetary penalties imposed for violations.
I don't think the U.S. government can compel companies to lie. It can, though, request them to.
If the NSA said "your servers were compromised by a state-sponsored scheme, and we'd like your co-operation in running counterintelligence operations" I think it would be fair for a company to say "yes". Particularly if part of the offer included help extracting infected hardware from said company's infrastructure.
As an aside, what do you think is draconian about such a law? It seems like there are reasonable arguments for why it would be in the national best interest to keep an ongoing investigation classified. In fact it seems like an unusually straight forward application of the cliche justification “for national security reasons.”
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
talks about Congress, not an executive branch. the latter can gag a person, or a company.
See, for example, https://en.wikipedia.org/wiki/New_York_Times_Co._v._United_S...
That would be bad enough, however the next step by the government would be to increase the fine amount, were Yahoo to hold out over time. Kick it up to $1 million per day and Yahoo would have folded no matter what. The problem is pretty straight forward: the government could push it as high as necessary to compel the result they wanted.