A Polish government agency said it’s working with Amazon.com Inc.c to improve conditions at its facilities amid union concerns of worker exploitation.

The State Labor Inspectorate held more than 50 reviews of Amazon’s warehouses and other centers since 2014, finding irregularities related to health and safety regulations, sanitary conditions and timely remuneration, the agency said Thursday. The retail giant, whose market valuation is nearing $1 trillion, has in past months also come under fire in the U.S. and elsewhere for the working conditions of its employees, including by Senator Bernie Sanders.

“The vast majority of recommendations from our inspections were implemented by Amazon, which helped to improve working conditions and eliminate irregularities with regards to legal protection and the safety of workers,” Wieslaw Lyszczek, who heads the inspectorate, told reporters in Warsaw. “We’ll strive for the conditions at Amazon to improve further and we will make this happen.”

The pledge followed a request for help from a group of Amazon workers, who complained of low wages and “working conditions that degrade human dignity,” according to Agnieszka Mroz from the Workers Initiative, a union operating in Amazon’s "fulfillment center" in Sady, Poland.

Mroz said that some Amazon employees spend almost all of their 10-hour shifts on their feet, walk almost 20 kilometers (12 miles) a day, lift heavy objects and have “barely any time to go to the toilet or get scrutinized while there.”

“It is our priority to always be fully compliant with all applicable labor laws, and if something isn’t up to present labor standards then we always look into it and act immediately,” said Marzena Wieckowska, a spokeswoman for Amazon in Poland, where the company employs 14,000 full-time employees and as many as 10,000 seasonal workers.