This is not about legislators disclosing their funding, but about requiring researchers to do so when commenting on potential regulations.
So someone who has done a study that found silica in cement is actually good for you, then they would have to disclose if the study was funded by a cement company.
Similarly, someone who did a study that found silica in cement was worse than cigarettes would have to disclose if their study was funded by the the Enviromental Defense Fund.
As someone else pointed out earlier, a lot of research in areas like this is going to be funded by one group or another so it is important to disclose these financial ties but it doesn't necessarily immediately negate the usefulness of the research.
But overall, the effect would likely be to weaken the usefulness of industry-funded research, which is probably why Lama Alexander and the other Republicans oppose it.