The co-founder of LinkedIn said on Monday that he will give up to $5 million to veterans groups as part of a crowdfunding campaign if Republican presidential candidate Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE releases his tax returns.

Reid Hoffman has pledged multiply whatever is raised in the effort, which is being run by an ex-Marine named Pete Kiernan, by five. Hoffman, who is worth more than $3 billion, has said he will match the amount raised up to $5 million.

The effort promises to give the money raised to veterans groups if the presidential candidate makes the document public by the third debate in mid-October.

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“The ingenuity of Kiernan’s proposal is how it gives Trump a strong incentive to act but doesn’t reward him directly for something he should have already done,” said Hoffman in a Medium post announcing his pledge. “Instead, men and women to whom all Americans owe a great debt of gratitude will benefit from any positive action he takes.”

Trump has said that he will not release his tax returns because he is currently under audit. But many have called for him to release the returns, which has become a standard practice among presidential candidates.

The LinkedIn co-founder has donated in the past to Democratic candidates as well as left-leaning outside groups.

But Hoffman’s pledge reflects the singular antipathy toward Donald Trump among Silicon Valley’s elite. Dustin Moskovitz, a co-founder of Facebook, recently promised to spend $20 million toward electing Democratic candidates.

“If Donald Trump wins, the country will fall backward, and become more isolated from the global community,” he said.

The Republican nominee has regularly derided tech companies and expressed little interest in tech policy while on the campaign trail.

He has, however, at least one high-profile support in Silicon Valley: Peter Thiel, a venture capitalist who was an early funder of Facebook and a co-founder of PayPal, spoke before Trump at the Republican National Convention this summer.