In a video posted on the X social media platform, Tusk called on employers to take practical steps to safeguard staff during the hottest part of the day.
"Imagine working for eight hours in temperatures that could reach nearly 40 degrees across Poland today," Tusk said. "That's why I have an urgent appeal to employers above all: take care of your employees, your co-workers and yourselves."
He urged businesses with air conditioning to use it freely and said workers should have access to cold drinking water, fans and shaded workplaces.
Tusk also encouraged employers to allow remote work where possible, modify working conditions or duties and, if necessary, suspend work during the most dangerous hours.
"If there is no other solution, you really should take a break, because when temperatures outside approach 40 degrees, this is about people's health and even their lives," he said.
Poland's Institute of Meteorology and Water Management (IMGW) on Wednesday issued heat warnings covering almost the entire country, with the highest-level alerts in force across large parts of central, southern and eastern Poland.
According to the weather agency, temperatures were expected to range from around 30 Celsius in the northeast to about 36 C in central Poland, reaching as high as 40 C in the southeast.
The heatwave has prompted many city and municipal offices to shorten opening hours or adjust working schedules on Wednesday, state news agency PAP reported.
Meanwhile, two major power plants operated by the Enea utility group have reduced output because of low water levels in the Vistula River, the company said.
Nearly 60 percent of Poles support introducing rules requiring shorter working hours or a day off during extreme heatwaves, according to a survey published last month.
Source: IAR, PAP