If it's structured like that, sure, but it'll not be done that way.

One approach is for a politician/candidate to hold a fundraising lunch/dinner/whatever, and charge for seats. Lobbyists and other folks who want to get access to the senator will buy those tickets and get their couple of minutes to talk about whatever issue is important to them.

Any direction on bill will almost certainly be of a more indirect nature.

It won't be: "Vote against municipal fiber rollouts, and $ISP will give your campaign $10k".

It'll be more along the lines of: "We'd find it difficult to support the campaign of someone who wasn't seen to be acting in our best interests. We think that this municipal fiber rollout is bad for $ISP."

I think corporate donors are held to the same limits as individuals: $2,800 per election to the candidate, $5,000 to their reelection committee. The rest (which still totals less than $500k) goes to state and federal party committees.

Where the unlimited contributions come in (think Citizens United) are Super PACs, but those aren't technically affiliated with candidates, and they can't contribute to the candidates. The freedom of speech angle on this is that corporations or individuals can spend this money on political ads, but it has to be independent of the candidates.

> is it illegal for me to agree?

Yes, or it was illegal for them; this exceeds campaign contribution limits.

It's rare that such large sums would go through the campaign-finance slot. Supposedly Biden received only $200k from the credit card industry for his awful bankruptcy "reforms". Of course larger bribes are paid, but they are less direct and less public. One method I've seen up close (I worked for Lucent back when they were in business) is to hire close relatives of favored politicians at vastly inflated salaries for "show-up" jobs for which those relatives had no observable skills. Those relatives would eventually transfer large portions of the millions they "earned" to the politician, but there was no hurry. In addition, there are sweetheart "investment" opportunities that somehow are only offered to politicians. We've all heard about the exorbitant "speaking fees". ISTR a mayor somewhere published a book and arranged for certain constituents to buy thousands of copies of it. Avaricious politicians have imagination.