Shares of Twitter  (TWTR - Get Report) fell sharply Thursday after a bearish analyst report raised questions about the social media giant's third-quarter outlook and whether it is spending enough on safety and security.

The price of Twitter's shares fell 4.3% to $35.87 after MoffettNathanson analyst Michael Nathanson doubled down on his bearish outlook on the stock and reiterated his sell rating.

The analyst took aim at Twitter's spending on the safety and security issues that have plagued the tech industry, arguing it isn't enough.

By contrast, Facebook  (FB - Get Report) has more than seven times as many employees working on security and safety issues as Twitter, he wrote.

"This fact goes to one of the central tenets of our Twitter "sell" call; they simply aren't spending enough," Nathanson wrote.

Nathanson also contends Twitter's valuation -- up 30% in 2019 -- "remains as stretched as ever."

"As we look into the second half of 2019, now seems to be an especially opportune time to sell Twitter," Nathanson wrote in his report, released Thursday. "Just based on the math, Twitter is approaching difficult top-line comps given the sharp recovery in its U.S. business in 3Q 2018."

A spokesman for Twitter declined to comment.

However, in a letter to investors in April, Twitter argued it had increased spending by 20% year over year on "health, conversation, revenue product and sales, and platform."

Twitter cited new systems that make it easier for users to report abusive content, which has resulted in a 2.5 times increase in the number of tweets removed.

"We are taking an even more proactive approach to reducing abuse on Twitter and its effects in 2019," the company wrote.

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