Are employers entitled to accomodate pregnant employees?

I am a cna who works 12 hour shifts at a hospital, I was 8 months pregnant and started having contractions. I had contacted my supervisor about cutting my work hours until i return from my maternity leave and was told to bring in a doctor's note. At the time I presented my job with 4 notes stating frequent breaks for hydration so the final note stated for me to work only 8 hours a shift and not lift over 20 pounds. My job said that they couldn't make the accomodations because they didn't have light duty and i was also told that if they accomodated me that they would also have to accomdate other employees that were seeking 8 hour shifts. So they basically informed me that i was being taken off the schedule and that i couldn't return until i had my baby. I want to know if this is discrimination due to pregnancy because I know of some employees who work 8 hour shifts and also a few who have been on light duty.