The U.S. dollar's surge this week has some investors worried that the stock market may be close to hitting a snag.
That concern isn't universal, but it's real for some market players and comes just as all-time highs for major U.S. stock indexes appeared to signal an all-clear for shares, and as corporate earnings are emerging from four straight quarters of declines.
"A strong dollar is going to hurt exporters. You could see that impact on their earnings," said Chris Gaffney, president of EverBank World Markets. "We saw some companies talking about a strong dollar earlier this year, and you could see that rhetoric pick up."
On Wednesday, the , a measure of the greenback's strength versus a basket of major currencies, climbed above 101.85 — to its highest level since March 2003.
U.S. dollar strength has gained momentum with the rise in Treasury yields since President-elect Donald Trump won the U.S. election. Trump boosted market expectations for economic growth by touting government spending and corporate tax cuts. The dollar index is up about 4 percent since the election, after erasing year-to-date gains beforehand.
"The more worrying thing to me is the momentum in the dollar post-election. If that continues, that's going to be worrisome," said Lee Ferridge, head of macro strategy, North America, at State Street Global Markets.
"If that were to persist from already high levels, I think you'd see a lot of corporates bemoan the higher dollar, and that would hit earnings," he said.
For the latest earnings season beginning in mid-October, 33 S&P 500 companies were already discussing concerns about the strong dollar in their earnings calls, according to AlphaSense, a financial search engine.
And on Wednesday, Hewlett Packard Enterprise CEO Meg Whitman said on CNBC's "Squawk on the Street" that "a strong dollar creates currency headwinds for us, as it has over much of the last three or four years."
The firm reported earnings late Tuesday that beat expectations by 1 cent a share, on revenue that missed. Guidance for the fiscal year was softer than many analysts had forecast.
For S&P 500 companies overall, 44.4 percent of sales come from overseas, according to S&P Dow Jones Indices.
Nearly 58 percent of sales for the energy and information technology sectors come from foreign markets, while the materials sector accounts for 53.5 percent of its total sales as coming from overseas, the data showed.
Lindsey Bell of CFRA Research estimated that a strong dollar hurts earnings per share by between 5 and 10 percent, depending on how strong the dollar is. She said a roughly 20-percent year-over-year rise in the dollar index last year probably was the largest negative impact on earnings in the second quarter of 2015, when earnings per share grew just 0.2 percent.
Some market players are playing down the significance of the rising greenback, however. Ben Pace, CIO at HPM Partners, said that "the dollar is strong for we think the right reasons … I think people tend to overreact to the strong dollar. It's the reason why it's strong that I think is important."
"If the dollar is stronger because of U.S. economic growth getting better … it could get offset by topline and bottom line earnings growth," he said. His latest forecast for U.S. 2017 gross domestic product stands at 2.25 percent, but he expects to raise that projection by between 0.5 and 1 percentage points.
The U.S. dollar index is also less than 2 percent higher year-over-year right now, compared with the surge that weighed on earnings last year.
"We're actually somewhat bearish on the dollar," said David Lefkowitz, senior equity strategist at UBS Wealth Management Americas. "From our perspective, the dollar looks fairly expensive."
"We haven't made any changes in light of the election," he said, noting the firm has continued to recommend stocks. "The market has been focused on the policies on the pro-growth aspect of the Trump policies (but not on the negatives), namely what happens on the trade front, what happens on the geopolitical front."
—CNBC's Matthew J. Belvedere contributed to this report.