A new wave of teacher strikes has highlighted a growing problem for all US workers – growing health costs which have become a “hungry tapeworm” on Americans’ wages.

In the most expensive health system in the world and the only industrialized nation without universal healthcare, more than 177 million Americans get health insurance through an employer. But insurance is rarely free.

“They’ve shifted the healthcare costs and the pension costs on to employees, so employees are making less and they’re spending less,” said Randi Weingarten, president of the American Federation of Teachers, which represents 1.7 million members. “It’s a double whammy.”

Conservative legislatures’ push to shift health and pension costs on to individual teachers means in some states, teachers take home less pay than they did five years ago.

The most high-profile example is West Virginia, where teachers earned a 5% raise after a nine-day wildcat strike. Before that, they earned less take-home pay than in 2012 because of soaring health costs.

Over the last decade, private insurance companies have increasingly demanded more “cost-sharing” from patients, a euphemism for more money out of people’s pockets. This week teachers in Oklahoma became the latest to take industrial action.

In 10 years, out-of-pocket costs have increased dramatically for all Americans. From 2005 to 2015, the average amount of money people have to pay themselves before insurance cover kicks in grew from $303 to $1,505. Once insurance starts paying, people are liable for another cost, called “coinsurance”. That grew from $134 to $253, on average. Overall, cost-sharing rose 66% in 10 years, according to Kaiser Family Foundation.

In the last decade, workers’ contract negotiations have orbited around health costs. What will an employer pay? Can the employee take on more?

“They are center stage in every contract negotiation,” said Weingarten. “I don’t know a contract negotiation where they haven’t been center stage.”

So extreme is the situation that a group of billionaires have set out “disrupt” health insurance because it would help their bottom line. Among them was investor Warren Buffett, who called health costs a “a hungry tapeworm on the American economy”.

Increasing health costs are not unique to teachers – Americans across the labor spectrum have paid more out-of-pocket for healthcare. However, conservative policies have inadvertently made them the most visible victims.

In states such as Arizona, Oklahoma, West Virginia and Wisconsin, conservative legislatures pushed for all teacher pay raises to go through the statehouse. Now, with mounting labor actions, it’s those same statehouses that face pitched battles to improve teacher benefits.

“The right wing thought if this would happen we would be less politically engaged,” said Weingarten. “But this requires you to be more politically engaged.”

In Jersey City, New Jersey, teachers cited the burden of health costs when they went on strike in mid-March. It was the first strike in 20 years.

“We want nothing more than to get back to work under a contract that respects the expertise of our members and the need for affordable healthcare,” said the teacher union president, Ronald Greco, according to NJ.com. Teachers are required to pay between 3% and 35% of their pay to health insurance, thanks to a recent state law.

A student enters the Academy I middle school in Jersey City, New Jersey, as teachers strike on 16 March. Photograph: Julio Cortez/AP

In Oklahoma, where teachers have the lowest average teacher pay of any state, a walkout started Monday. The state pays for health insurance for employees. Benefits for their families cost extra, but that care is constantly under threat.

“The state will start complaining that the cost of healthcare keeps rising and it’s becoming burdensome,” said Ed Allen, the president of the Oklahoma City American Federation of Teachers chapter. “They will do comparisons with other states and say their salaries are much higher, but they don’t pay as much on the healthcare.”