A trader works on the floor at the New York Stock Exchange (NYSE) in New York City, U.S., June 18, 2026.

Jeenah Moon | Reuters

The S&P 500 fell on Monday, weighed down by declines in technology stocks and SpaceX. Wall Street also assessed the latest developments in the Iran war negotiations and awaited the release of inflation data closely watched by the Federal Reserve.

The broad market index fell 0.3%, while the Nasdaq Composite declined 1.1%. The Dow Jones Industrial Average added 167 points, or 0.3%.

Major tech names pulled the market into negative territory. Shares of Alphabet dropped 6%, while Amazon and Meta Platforms lost 4% and 2%, respectively. Microsoft shares also declined 2%.

SpaceX was another laggard. The stock fell 8%, putting it on pace for its third straight daily decline.

However, Micron Technology was one of the outperformers, rising more than 3%. The move comes ahead of the chipmaker's quarterly report, due Wednesday after the bell. Fellow chipmakers also saw gains, with Advanced Micro Devices moving up 1% and Intel adding 3%.

Brent oil futures turned negative on Monday after mediators Qatar and Pakistan said that U.S. and Iranian officials had agreed on a roadmap to reach a final deal within 60 days. Oil prices later traded around session lows after the Treasury Department authorized the sale of Iranian oil for 60 days.

International benchmark Brent crude futures for August fell more than 3% to around $77 a barrel. U.S. West Texas Intermediate futures for July were more than 2% lower at roughly $74.

A key test for the market this week will be the release on Thursday of May's reading on the personal consumption expenditures price index, the Fed's preferred inflation gauge. Even excluding volatile food and energy prices, core PCE is expected to increase from April, according to economists polled by FactSet.

Following last week's hawkish Fed meeting, expectations of an interest rate increase were pulled forward to as soon as October. Investors are now laser-focused on any inflation reading that could signal the U.S. central bank may soon begin hiking rates.

While Fundstrat Global Advisors' Tom Lee believes a number of catalysts could impact the market down the line – such as the implementation of task forces at the Federal Reserve and supply chain impacts from the closure of the Strait of Hormuz – the environment remains positive.

"We still believe later this year there is going to be an abrupt change of market conditions, one that feels very much like a bear market, but we don't want to stand and call a top," the firm's head of research said on CNBC's "Closing Bell" on Thursday. "I think conditions are still favorable for stocks."