Bernie Sanders’ plan ends the ability of corporations to shift profits offshore by taxing them wherever they are generated in the year in which they are earned. Donald Trump’s tax plan also ends to the deferral of taxes on corporate income earned abroad and charges a one-time, 10% tax on cash held overseas so it can be repatriated. Both will leave the foreign tax credit in place so companies will not face double taxation.

Both plans are likely to generate significant revenue. According to a March 3 report from the Citizens for Tax Justice (CTJ), Fortune 500 corporations are avoiding up to $695 billion in U.S. federal income taxes on $2.4 trillion in offshore holdings. While this figure is higher than “official” estimates—a report by the Congressional Research Service estimated that large corporations are avoiding $100 billion in US taxes—the CTJ uses a number of assumptions based on company accounts to create a more complete picture of corporate tax avoidance.

For example, it notes that Pfizer (PFE), which has subsidiaries in the Cayman Islands, Ireland, the Isle of Jersey, Luxembourg, and Singapore, holds almost $200 billion in what is called unrepatriated income. This is not disclosed directly anywhere in Pfizer’s accounts, but since the company estimates, in a footnote, a figure for the deferred taxes it would owe if it brought the cash back to the U.S., the CTJ worked backwards to calculate a total offshore cash figure. Pfizer’s contemplated tax inversion, whereby it would reincorporate in Ireland, would move this cash permanently offshore.

Trump and Sanders are also both against tax inversions.

According to the CTJ report, Pfizer appears to be one of the companies most aggressively moving cash overseas, since its estimated offshore cash rose from $176 billion in 2014 to $194 billion in 2015. (A Pfizer representative said the company was unable to confirm or deny the figures because it did not know the methodology being used by CTJ.)

Apple is another such company. Its offshore cash, which it calls “cash, cash equivalents and marketable securities,” rose from $158 billion in 2014 to $200 billion in 2015, the CTJ says. Apple (AAPL) declined to comment for this story and referred me to the company’s annual report. However, CTJ’s figures come from the company’s latest quarterly report. Fortune was able to confirm those figures.

But what makes it so difficult to estimate the amount of lost tax revenue? Firstly, only 55 companies in the Fortune 500 disclose, like Pfizer, how much tax they would have to pay if they brought the cash back home. The vast majority make no such estimate.

General Electric, for example, disclosed holding $104 billion offshore at the end of 2015. GE (GE) has subsidiaries in the Bahamas, Bermuda, Ireland, and Singapore, but it does not disclose how much of its offshore cash is held in these tax havens, all of which have either very low or no corporate tax rates. Asked for comment, a GE spokesperson suggested that the goal wasn’t tax avoidance. “This is not $104 billion of cash holdings in bank accounts—these are earnings we have reinvested in our businesses,” the spokesperson said. “We are in 180 countries and these holdings allow us to fund operations like factories and R&D centers in other countries, which help us win more business.”

Many such “non-disclosing” companies claim an accounting loophole that allows them to say calculating the likely tax rate on repatriating the money is “not practicable.”

Sanders notes that one five-story office building in the Cayman Islands is the “home” to more than 18,000 corporations. That even a small proportion of this amount of cash is being earned in these locations, however, is unlikely. A 2014 CTJ study found that US corporations “collectively report earning profits in Bermuda and the Cayman Islands that are 16 times the gross domestic products of each of those countries, which is clearly impossible.”

If the Securities and Exchange Commission required more complete disclosure about multinationals’ offshore profits, the loss of revenue would be much more widely known, and the case for ending tax deferrals would be much stronger. In contrast to Sanders and Trump, however, corporations are lobbying government to give them a tax holiday so they can repatriate the offshore cash without paying any U.S. tax on it.

That’s not an advantage regular Americans get, which makes it easy to argue that if corporations are citizens they should pay taxes like citizens, on their income and in the year in which it is earned, regardless of where it is earned.