"We had a strong market in the past week, and what generally happens in the first week sets the trend for the remainder of the year. Now that it's established, there could be some profit- taking," said Peter Cardillo, chief market economist at First Standard Financial in New York.
At 9:41 a.m. ET (1441 GMT), the S&P 500 was down 2.84 points, or 0.10 per cent, at 2,740.31.
The Dow and the Nasdaq still eked out record highs briefly after open.
The dollar inched higher against a basket of major peers with data showing that slower US jobs growth did little to dent expectations for further interest rate increases this year.
Comments by some Federal Reserve officials on Friday and over the weekend suggested the US central bank remained on track to raise interest rates in 2018.
"The dollar is reversing and we're seeing that effect due to some Fed comments," Cardillo said.
A stronger dollar tends to weaken revenue of US companies that earn much of its income from abroad.
Investors are waiting for earnings reports to see how much companies would benefit from the recent tax cuts. The fourth quarter earnings season will kick off later this week, starting with big banks.
Bank of America, Goldman Sachs, JPMorgan and Wells Fargo were down between 0.4 per cent and 1 per cent. Most big US lenders have estimated one-off charges to their fourth quarter earnings on account of tax cuts.
Shares of Nvidia climbed about 4 per cent after the graphics chipmaker announced partnership with Uber and Volkswagen as its artificial intelligence platforms expand into technology for self-driving cars.
Declining issues outnumbered advancers on the NYSE by 1,659 to 971. On the Nasdaq, 1,711 issues fell and 860 advanced.