Metro apologized to Nichole Hakimian for the inconvenience, but said a review found the driver did not break any rules.
The mother said she is not interested in any apology, and plans to take legal action.
"You don't just come out of nowhere and kick a mom off a bus with a sick child," she said.
Hakimian said a Metro driver told her and her 1-year-old son to get off two stops before her destination. She was headed to a medical clinic in Seattle's Beacon Hill neighborhood at the time.
"I said, 'He has diarrehea. I'm on my way to a doctor's appointment for him. She said, 'I'm sorry. It's unbearable. You need to get off the bus,"' she said.
Hakimian said the driver insisted she get off even when she told the driver she only had two more stops to go.
"She said, 'Well, I'm sorry. It's just unbearable. You need to get off the bus,'" she said. "Nobody (else) on the bus was complaining at all."
Metro released the following statement:
"This is a very unique situation. Our goal is always to balance the comfort of all of our riders with providing good customer service. The driver didn't violate Metro policy - she felt she had to advocate for her passengers by politely and apologetically asking the woman to exit the bus."
The mother is not happy that Metro will not act.
"You need disciplinary action, and I think they went about it the wrong way," she said. "When you do something wrong - no matter what it is, no matter what circumstance - you need to be punished for that."
Metro said the driver in question has been an employee for 9 years and has an excellent record.