Has Sen. Bernie Sanders really been lying about Hillary Clinton's donor base?

That's the accusation Clinton made during a testy exchange March 31 with a Greenpeace activist when Clinton was asked while shaking hands with people if she would start rejecting fossil-fuel money in her campaign.

"I do not have," Clinton said, then stopping herself and beginning again. "I have money from people who work for fossil fuel companies. I am so sick. I am so sick of the Sanders campaign lying about me. I’m sick of it."

Clinton wasn't specific about the alleged lie she was talking about, and her campaign didn't give a specific answer when we asked.

However, the Sanders campaign responded with a new release saying, "The truth is that Secretary Clinton has relied heavily on funds from lobbyists working for the oil, gas and coal industry."

Sanders spokesman Michael Briggs cited analyses by Greenpeace and the Huffington Post .

The Clinton campaign, in return, asserted that "Hillary Clinton’s campaign has not taken a dollar from oil and gas industry PACs or corporations." PACs are political action committees.

This is important because, according to Sanders, accepting such contributions means the fossil fuel industry would have undue influence over Clinton’s energy policy.

Clinton has said in the past that if individuals from the industry want to donate to her, they should know that they may be wasting their money. She favors policies the oil and gas industry don't like, and she is a big supporter of renewable energy, a philosophy Sanders has also embraced.

With so many accusations flying around, we thought it was important to lay out the facts of the matter.

Neither Clinton nor Sanders — or any other presidential candidate, for that matter — can accept money from fossil fuel companies (or any other corporation). That would be illegal under federal campaign finance laws.

So all the money in the coffers comes from individuals. The limit for this election is $2,700 per candidate per election (the primary and general election count separately). Political action committees can donate $5,000 per election to a candidate.

In fact, people in the fossil fuel industry have given to both campaigns, though they’ve donated more to Clinton.

According to the latest tallies from Center for Responsive Politics , Clinton's campaign has received $307,561 from people who work for oil and gas interests so far in the presidential race. Sanders has received nearly six times fewer dollars — $53,760.

For Clinton, that's 0.2 percent of the more than $159.9 million her campaign committee, Hillary for America, has raised. For Sanders, it's 0.04 percent of $139.8 million.

Super PACs supporting Clinton have directly given an additional $25,701. Sanders does not have a super PAC.

So far, 97.7 percent of donations from people connected the oil and gas industry have gone to Republicans.

But in Clinton’s case, that doesn't include " bundlers ," a fancy name for fundraisers who collect money from individual donors and bundle the money together for a campaign.

A bundler might, for example, arrange to have each executive from an oil company, along with each adult member of his or her family, give $2,700 per person, which is bundled together and given to the campaign. It's legal because the individuals aren't violating the per-person limit.

The Huffington Post article from July 17, 2015, cited by Sanders found that "nearly all of the lobbyists bundling contributions for Democratic presidential candidate Hillary Clinton’s campaign have at one time or another worked for the fossil fuel industry." It links to 40 registered lobbyists but only offers details on some donors who still work for the industry.

However, the Greenpeace report says that when you add in the bundlers’ donations (lobbyists with some alleged tie to the fossil fuel industry), Clinton's total rises to nearly $1.8 million. The fossil fuel industry's share of the Clinton coffers goes up to 0.8 percent.

The Greenpeace report goes a step further to include $4.25 million going to Priorities Action USA, the super PAC that supports Clinton.

But it’s a stretch to draw a direct line between those super PAC donations and Clinton’s campaign. Under federal law, the candidates have no control over super PAC spending.

Those are the issues and dollars at play. We’ll continue to watch the accusations on this issue from both campaigns.

(An earlier version of this story gave the wrong percentage for the amount of money Sanders has received from people connected with the oil and gas industry. It has also been updated with the correct contribution limits for the 2016 election.)