Wall Street has been in rally mode for a while now, but Monday brought a pause in the recent gains for major stock market benchmarks. The Nasdaq Composite (NASDAQINDEX:^IXIC) was down about two-thirds of a percent at 10:30 a.m. EDT, pulling back from a recent run that came close to challenging the index's record highs.

The Nasdaq's performance has hinged largely on how well some of the biggest and most influential companies in the stock market have done from a business standpoint. On Monday, shares of Tesla (NASDAQ:TSLA) pulled back on news regarding a car crash and its Autopilot system. Meanwhile, NVIDIA (NASDAQ:NVDA) has been trying to move forward with a planned acquisition, but regulators are looking askance at the deal and asking questions that might be tough for the chipmaker to answer to their satisfaction.

Tesla hits the brakes

Shares of Tesla fell almost 6% on Monday morning, dropping below the $700-per-share level. The electric automaker was under pressure amid news of a fatal vehicle crash over the weekend.

Four Tesla vehicles in different colors in a clearing in a desert landscape.

Image source: Tesla.

Over the weekend a Tesla Model S crashed into a tree after unsuccessfully navigating a bend in a road just north of Houston, according to reports. When first responders arrived to put out a fire that resulted, they found that no one was in the vehicle's driver's seat. One passenger was in the front and another in the back.

This isn't the first fatality linked to Tesla's driver assistance platform. Back in 2016, a Florida driver died after the Model S he was driving crashed into a turning truck while the Autopilot mode was engaged. According to reports, the vehicle never slowed down before impact.

Tesla has maintained that its vehicles are safe and that in the long run, autonomous vehicle and driver assistance systems will be at least as effective in avoiding accidents as human-driven vehicles. Each time an accident happens, though, worries rise that regulators might take steps slowing the pace of autonomous vehicle innovation both for Tesla and for other automakers.

Will the U.K. stop this NVIDIA deal?

Elsewhere, NVIDIA shares were down a bit more than 1%. The semiconductor giant faced a new setback in its efforts to acquire chip design specialist ARM Holdings.

Regulators in the U.K. have said that they will look at the potential impact of NVIDIA's acquisition of ARM in the context of national security. The first step involved the filing of an intervention notice that will start the clock on gathering additional information regarding the $40 billion deal. Evaluation could take months, with an initial deadline near the end of July for the filing of a report. Upon completion of the report, regulators will decide whether to allow the deal to move forward or conduct an even longer inquiry.

The NVIDIA-ARM acquisition has been controversial for a while. Several of the largest tech companies in the world have opposed the sale by Japan's SoftBank (OTC:SFTB.Y), citing the potential threat to their existing licensing deals with ARM.

At best, the regulation further delays what could be a strategically important acquisition for NVIDIA. At worst, what U.K. regulators find will either force major changes to the terms of the buyout or even kill it entirely.

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