Can an employer make an employee have insurance to continue with employment?

I'll try to make this short and sweet. If you need more detailed information, or know where to point me in regards of asking the right person, feel free to send me an email. Thanks for your help! So, I recently got a job working with developmental disabled adults. I make $9/hour, work 40 hours a week (full time employee). I recently completed my 90-day probation period and am now eligible for the insurance my company offers. Yesterday, I went to pick up my paycheck and was handed all the paperwork to fill out. I was looking through it and I came across this form that said that I am giving my company permission to deduct $91 from my check every month to cover my portion of the medical/dental premium. Previous jobs I've had I've always paid for insurance every month that I never use (I hardly get sick, I don't have kids) So in all actuality, I'd rather not have insurance. My boss then asked me today if I had my paperwork ready to go and I told her I wasn't interested, she then told me that I can't work there if I don't have insurance. That seems weird to me. I was never disclosed this when I was hired at all. And I didn't have insurance from hire day 1 to hire day 90. So what's the difference now? Basically I want to know if it's fair/legal that I MUST have insurance to keep my job?! I work in Washington State.
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NO they are NOT allowed to require you to accept their company provided insurance, especially in light of the fact that they are asking you to pay for part of it. Not that it's illegal or even wrong that they are asking you to cover some of the costs, but they cannot require you to sign up for something that costs you money! Before going to the dept. of labor, talk to your HR person first. Make sure that your boss is correct that they REQUIRE you to take their benefits before you jump the gun on this one. However, if you verify that they DO require it, take my suggestion listed below: Go to the Washington State Dept. of Labor & Industries page (see link below). This link will take you to the FAQ's page regarding what is acceptable regarding deductions from pay. It explains that the deductions listed (medical is included here) are acceptable as LONG AS THEY ARE AGREED TO. Contact the dept. of labor and tell them your employer is threatening to fire you for not taking their benefits. Although they do not regulate benefits, they do regulate unlawful deductions and this sounds like it would not be voluntary if they are threatening to fire you! http://www.lni.wa.gov/WorkplaceRights/Wa… Good luck to you!
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