The United States Postal Service has apologised and launched an investigation after an employee was accused of shouting “speak English” to Spanish speaking customers.

In Pilsen, Illinois - in a neighbourhood that is home to many immigrants and a building named after Cesar Chavez - a postal service employee has reportedly been turning away customers if they don’t speak English.

Evelyn Gonzalez, a customer at the post office, told ABCNews7 she saw four instances of the employee refusing service to individuals.

Ms Gonzalez wrote about her experience in a Facebook post which gained traction online.

“With a very loud, bad attitude she would say ‘Speak English,’ and ‘I’m not going to help you,’” Ms Gonzalez said.

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The employee would even get angry when other customers would try to help the non-English speaking individuals that had been turned away, according to Ms Gonzalez.

“I asked the lady ‘a donde quiere, mandar esta paquete?’ ‘Where do you want to send this package to?’ The customer said Mexico. [The employee] right away, without hesitation, said ‘No, I can’t help you. I’m not going to help you,’” Ms Gonzalez said.

The four instances observed by Ms Gonzalez weren’t the only reported incidents from the post office. Ward Alderman Byron Sigcho-Lopez investigated the claims further and found several residents who reported similar treatment.

“The post office in a city like Chicago, a welcoming city, we need to make sure we have the proper services, bilingual staff and that materials are translated in all languages to guarantee good service for all residents,” Mr Sigcho-Lopez said.

Tim Norman, a United States Postal Service spokesman, confirmed that there were no bilingual clerks at the office in Pilsen and that employees who face language barriers are instructed to use translation tools like Google Translate to help serve customers.

“This reported incident is being fully investigated and the postal service will take appropriate action,” Mr Norman said. “I would like to also add that we are actively seeking bilingual employees to work at stations such as Cesar Chavez.”

The USPS issued a full statement in response to the reports: “We were recently made aware of an incident at our Cesar Chavez Post Office last week which involved one of our employees denying service to some of our Spanish speaking customers. We want to sincerely apologise to any and all our valued customers who were affected by these actions and denied service. This reported incident is being fully investigated and the Postal Service will take all appropriate action necessary to improve service to our valued customers. The Postal Service expects all of our employees to treat each other and our customers with dignity and respect and we will work to identify any concerns and make corrections to better serve our customers.”