Just weeks after closing all its company-owned stores to conduct anti-bias training, a Philadelphia Starbucks is in hot water after a barista allegedly mistreated a customer with a speech impediment.

A worker at a cafe in University City is accused of mocking a man with a stutter, according to an NBC affliate.

Tan Lekwijit, a Wharton student, described the June 27 incident in a post on Facebook saying that his friend Sam, a 28-year-old University of Pennsylvania graduate student, stuttered when he told the barista his name after ordering a coffee. The barista reportedly replied, "Okay, S-s-s-sam" and when Sam retrieved his coffee the cup had "SSSAM" printed on it.

"I am writing this not because I want to get anybody into trouble, but because I want to raise awareness among the employees," Lekwijit wrote on Facebook. "There are many people with speech disorders who are in a worse position than my friend’s and struggle with self-esteem and self-confidence. Getting this kind of treatment from people, especially service employees, only scars them — and I beg Starbucks employees to have this in mind."

According to Lekwijit, Sam reached out to Starbucks Customer Service, which apologized and offered $5 in compensation.

"We want our stores to serve as a welcoming place for everyone who visits and want to ensure our partners provide a positive experience," a Starbucks representative wrote on Lekwijit's Facebook post. "Our local leadership has reached out to Sam to better understand what took place and the specifics of his experience and apologize directly. We have zero tolerance for discrimination and are addressing this immediately."

In a statement to CNBC, Starbucks said: "Our local leadership has reached out to the customer to better understand what took place, the specifics of his experience, and to apologize for his experience directly."

This incident comes just three months after two black men were arrested at a different Starbucks in Philadelphia after asking to use the restroom and not ordering anything while they waited for a friend to arrive.

In response, Starbucks conducted an afternoon-long anti-bias training session with more than 175,000 employees in May. The training hoped to raise awareness among its staff about subconscious biases they may hold against people of different races, ethnicities, religions, genders and sexual orientation. The goal was to make Starbucks cafes more inclusive.

It was not immediately clear what, if anything, was said about disabilities.

The company announced earlier this week that it plans to roll out its new training program over the next year with six separate courses for managers and six for employees. These additional training sessions will address engaging with empathy, gratitude and building diverse teams.

Separately, the New York Post reported Starbucks' deputy general counsel in charge of ethics and compliance, Matthew Shay, a 21-year veteran of the company, retired at the start of June. Starbucks told the paper the exit was planned.