Elon Musk, who is worth $19 billion, turns 48 on Friday. He certainly could afford to throw himself an over-the-top birthday party. But according to Musk, that's not what he'll be doing.

Musk says he will be working.

When a Twitter user asked Musk, "Any big birthday plans?" on Thursday, Musk responded: "Working on Tesla global logistics."

TWEET: Working on Tesla global logistics

"You need time off too, don't you?" replied the same Twitter user.

The tech billionaire responded with a frowning face.

TWEET: :(

He said he would accept a party on Twitter from his followers, however.

TWEET: Ok, thanks

The working birthday may be due to Tesla's second quarter goals. On Tuesday, Musk sent an email to his entire staff there asking them to work hard to hit those vehicle production and delivery numbers. At the end of the first quarter of 2019, Tesla said it expected to deliver between 90,000 and 100,000 vehicles in the second quarter.

"As you may have noticed, there is a lot of speculation regarding the vehicle deliveries this quarter. The reality is that we are on track to set an all-time record, but it will be very close. However, if we go all out, we can definitely do it!" Musk wrote in the email, obtained by CNBC.

The effort remaining is primarily logistics, Musk said in his all-staff email.

"We already have enough vehicle orders to set a record, but the right cars are not yet all in the right locations. Logistics and final delivery are extremely important, as well as finding demand for vehicle variants that are available locally, but can't reach people who ordered that variant before end of quarter," Musk said.

The second quarter goes through the end of June.

TWEET: There are way easier places to work, but nobody ever changed the world on 40 hours a week

Musk has previously positioned himself as the leader who struggles on the front line with his employees.

In the summer of 2018, when Tesla was ramping up production of its Model 3, Musk stayed on location to diagnose and fix problems in the factory production line. He called the time "painful" in conversation with "CBS This Morning" host Gayle King.

"Absolutely, of course. Yeah, I'm sleeping on the factory floor, not because I think that's a fun place to sleep. You know. Terrible," he said. "I don't believe like people should be experiencing hardship while the CEO is, like, off on vacation," Musk told King.