An oppressive heat wave that has been baking Texas in record temperatures is predicted to move north and east this weekend, bringing stifling heat and humidity to states from Missouri to Florida. The desert Southwest and central California are also expected to see dangerously high temperatures.

As of Thursday, at least 15 people in the U.S. had died from heat-related illnesses, reported The New York Times.

Temperatures are expected to rise to as high as 20 degrees hotter than the normal average in the South, at least through the weekend, with the heat index — the combination of temperature and humidity — climbing even higher.

When high humidity combines with oppressive heat, it becomes more dangerous. The body can’t cool itself off as well by sweating, which is when heat exhaustion, cramps and heat stroke become a concern, especially for vulnerable people like young children, the elderly, individuals with some medical conditions and those who are pregnant. This is especially true when the heat index is 90 degrees Fahrenheit or higher.

In most of the U.S., there are no protections for workers toiling in the heat either outdoors or in buildings with no air conditioning, and during the latest heat wave in Texas, some decided to walk off the job.

“When I came in, it really was so hot. I decided I need to go on strike. I told my co-workers because it is way too hot here and I knew they were all extremely hot as well,” said Gloria Machuca, a former McDonald’s employee in Houston, as a heat dome sat over Texas last week, as The Guardian reported. “If we don’t work, they don’t make money. They’re making money off our sweat and it’s not fair. It’s time they truly value us.”

Read the full article about heat waves and climate change by Cristen Hemingway Jaynes at EcoWatch.