Ahead of the Wednesday afternoon announcement, an administration official told Reuters the proposal would include a sharp reduction in the tax rate from the current 35 percent to 10 percent for repatriation of profits — overseas earnings brought back to the U.S.
However, the memo from the White House just stated, "one-time tax on trillions of dollars held overseas."
Treasury Secretary Steven Mnuchin said the actual rate has yet to be determined and that the White House is "working with the House and Senate" on a repatriation rate, saying it would be "very competitive."
"The market had big expectations. They were expecting a lot of specifics and a specific rate on repatriation and they're not getting it," said Lawrence McDonald, author of "The Bear Traps Report" newsletter.
The repatriation tax "is definitely coming, they just don't want to show their whole hand to the Democrats," he said.
Apple shares intraday performance (beginning from around noon ET)
Apple, Microsoft, Alphabet,
Technology is the top performer in the S&P 500 for the year so far and the second best performer since the election — financial stocks are still the first.
Many on Wall Street have expected that much of any repatriated cash would go towards share buybacks.
Back in November, after Trump's election win, Goldman Sachs' chief U.S. equity strategist David Kostin forecast that S&P 500 buybacks would surge by 30 percent this year if there is repatriation, but by just 5 percent without tax reform. Kostin estimated that lower tax rates on repatriated profits should add $150 billion to a total expected $780 billion in buybacks, only the second time in 20 years for which buybacks will account for the largest share of total cash use by S&P 500 companies.
Apple has also topped the list of S&P 500 companies with the largest quarterly buybacks and share count reduction in history, according to Howard Silverblatt,
— CNBC's John Melloy and Jacob Pramuk contributed to this report.
Watch: Challenges to Trump's tax plan