Exactly how is requiring groups who engage in lobbying and who presume to weigh in on scientific debate to reveal their actual sources of funding censoring speech in any meaningful sense of the phrase?
Because putting "conditions" on speech is changing it from a fundamental freedom that governments should recognize, into a privilege that governments may (or may not) grant.
they're trying to hide the fact that they're paid whores of the fossil fuel industry.
Whores have rights too.
What's being questioned is their integrity
You have a right to question their integrity. You do not have a right to silence them. Integrity is not, and should not be, a pre-condition for Constitutional rights to apply. Scumbags have rights too.