NEW YORK (TheStreet) -- Stocks were modestly lower by late afternoon Monday, backing off from Monday's rally and feeling the pressure of uncertainty over a Iran nuclear deal. 

The S&P 500 was down 0.53%, the Dow Jones Industrial Average slid 0.45%, and the Nasdaq fell 0.55%. All benchmark indexes added more than 1% on Monday.

Crude oil prices fell as negotiations between Iran and six world powers over a nuclear deal looked to continue into Wednesday's session. Conversations may continue tomorrow, "if necessary, as long as the conversations continue to be productive," White House spokesman John Earnest said Tuesday.

If passed as proposed, Iran will be restricted from developing nuclear weapons in exchange for the lifting of economic sanctions. Easing sanctions would mean the release of Iranian oil into an already-oversupplied global commodity market. West Texas Intermediate crude oil on Tuesday fell 1.9% to $47.77 a barrel.

However, some economists argue the reaction to potential Iranian crude adding to global markets in the near term may be an over-exaggeration.

"Although Iran may have a sizeable inventory in floating storage ... ready to be released upon the lifting of oil sanctions, the reality is that it would still be a gradual and protracted return of its production to the global market in the next year or so as flows ramp up," said Schneider Electric commodity analyst Matt Smith.

The U.S. dollar continued to climb against other major international currencies, looking to close out its best quarter since 2008. The euro headed for its worst quarter on record, down around 11% since January as the eurozone and U.S. diverge in monetary policy.

On Tuesday, the U.S. dollar gained 0.83% against the euro, 0.48% against the Aussie dollar, and 0.53% against the Swiss franc. A higher U.S. dollar has the potential to limit earnings growth at a number of U.S. multinationals. 

Consumer confidence jumped to 101.3 in March, according to the Conference Board's monthly survey. That was an improvement on February's 98.8 reading and better than an expected 95.5. Confidence hit its highest level since before the Great Recession in January.

"There's still confidence out there from the consumer. Despite what we saw in yesterday's spending numbers, they are feeling confident about their current positions," said Calvin Silva, senior retail specialist at Nasdaq Advisory Services, in a call. "It paints the picture of consumers continuing to strengthen their own personal balance sheets. 

Consumer spending was up just 0.1% in February, missing economists' estimates, though recovering from two straight months of declines. 

Business activity in the Chicago region grew to 46.3 in March from 45.8 a month earlier, according to the latest Chicago PMI figures. However, the reading remains below the 50 level indicative of contraction for its second straight month.

Residential real estate values grew 4.6% year over year in January, according to the S&P Case-Shiller 20-city home price index, despite harsh winter weather. Denver and Miami saw the biggest gains over the past year, up 8.4% and 8.3%, respectively.

"The economic data has been unquestionably mixed and there's little doubt in our mind that first quarter GDP, continuing a trend we've seen for much of the recovery, will be quite weak," said BTIG chief strategist Dan Greenhaus. "Today's data doesn't do much to change that overrding narrative and as we progress through the year, we think economic data will end up somewhere in-between the strong jobs numbers and weak-everything-else."

Charter Communications (CHTR) - Get Report surged 6.3% after announcing it will acquire Bright House Networks for around $10.4 billion. Bright House has approximately 2.5 million cable subscribers.

U.S. Steel (X) - Get Report dropped 3.7% on news it will temporarily idle its Minntac plant of its Minnesota Ore Operations, effective June 1. The company said the move was due to "challenging market conditions."

Priceline (PCLN) added 1.9% after being upgraded to buy from hold at Stifel. The firm said after a recent pullback, the stock is at an attractive level, particularly given European headwinds have now been priced in.

IBM (IBM) - Get Report moved 0.7% lower after announcing it will invest $3 billion over the next four years building an "Internet of Things" unit. The division will aim to develop technology to gather and analyze real-time data.

J.C. Penney (JCP) - Get Report spiked 7.9% after Piper Jaffray raised its price target on the department store retailer to $14 and increased its comp estimates for the first quarter. Analysts said the increase was on favorable weather conditions compared to last year.

Philips (PHG) - Get Report slid nearly 2% after agreeing to sell an 80.1% stake in its lighting division to Go Scale Capital for $2.8 billion.