U.S. stock index futures slipped Monday as renewed tariff uncertainty unnerved investors after President Donald Trump announced a new 15% duty despite a Supreme Court ruling that struck down his broader levies.

The Supreme Court, in a 6-3 ruling on Friday, voided most of the tariffs Trump imposed last year, finding that the emergency law he relied on did not allow the imposition of tariffs.

Using a different statute, Trump announced first a 10%, then a 15%, global levy that could last five months while the administration searches for more durable workarounds.

"It's really hard from a business standpoint when you are at a company to know how do you plan if you're not even sure about suppliers, supply chains and what the tariffs are going to look like," said Arthur Laffer Jr., president of Laffer Tengler Investments.

"That's a huge concern for corporate America and why it was really important to get that hammered out and ironed out as fast as possible, so that companies know what the playing field really looks like, and they can plan accordingly."

All three main stock indexes clocked weekly gains on Friday as markets took the Supreme Court's decision in stride, with the Nasdaq snapping a five-week losing streak.

At 6:37 a.m. EST, Dow E-minis were down 127 points, or 0.26%, S&P 500 E-minis were down 17.5 points, or 0.25%, and Nasdaq 100 E-minis were down 100.75 points, or 0.40%.

Most megacap and growth stocks were lower in premarket trading, though Alphabet bucked the trend with a 0.5% gain after gaining around 4% on Friday.

Nvidia kicked off the week 0.2% higher, heading to its quarterly earnings due on Wednesday. Commentary from the world's largest company by market capitalization could offer key insight about the AI sector that has been hit by growing investor skepticism.

High stock valuations and AI disruption fears have lately pressured technology and other sectors, as investors question if massive AI spending is paying off.

Earnings from major software firms including Salesforce and Intuit will be on the radar later this week, given that the S&P 500 software and services index has slumped more than 20% this year amid growing AI disruption fears.

Among early movers on Monday, Eli Lilly rose 4% after rival Novo Nordisk's obesity drug fell short against Lilly's drug in a Copenhagen trial.

Cryptocurrency and blockchain-related stocks dropped as bitcoin lost around 2%, with exchange operator Coinbase Global and crypto hoarder Strategy falling more than 1% each.

Gold and silver miners were broadly higher as prices of both precious metals gained. Top gold miner Newmont climbed 1.1% while silver miner Hecla Mining added 2.5%.