Warren used the exchange to highlight policy differences between her and her conservative colleague, including on paid family leave and increasing the minimum wage.
In the email screenshot by Warren, Cruz said that the personal sacrifices he's made to run for president include receiving negative attacks from the media and opponents, not spending time with his wife and daughters, limited sleep and personal time.
"The sacrifices for our campaign are steep, but I'm proud to be making them on your behalf," Cruz wrote. "You think of this the least, but as a candidate, my days are no longer my own ... There is almost no personal time when you run for president."
Warren, who commands a strong liberal following, accused the Republican presidential candidate of "whining" about problems that many Americans face.
"Are you kidding me? We're supposed to pity him because trying to be the leader of the free world is hard?!" Warren wrote in her post. "I've got two words for you, Ted: Boo hoo."
The Cruz campaign did not immediately respond to a request for comment.
Warren's critique of Cruz noted that there are American workers who don't receive paid leave and have to work even when they are sick.
"He opposes mandatory paid family and medical leave and calls it 'free stuff,' " she wrote.
She also said that there are American parents who work minimum-wage jobs to support their families and don't have personal time either because they struggle to make ends meet.
"And know who's facing constant attacks, Ted? Hardworking American immigrants, Muslims, LGBT folks, women. They're facing the GOP's constant attacks. They're facing YOUR constant attacks," she said.
"Senator Cruz -- you chose to run for President. Working people don't get a choice," Warren said. "Maybe you should spend less time complaining about your 'significant sacrifices' -- and more time trying to do something about theirs."