on mat leave, laid off due to lack of work?

I work for a small heating and air conditioning company approx 35 people are employed. I am on maternity leave. I delivered my son on 1/25. I was put on bed rest per the dr 1 week before delivering. I pay aflac for short term disability and they pay 8 weeks of maternity leave. I scheduled through my employer to come back to work on 3/28. They called me on 3/22 and said that they had lack of work and that they were laying me off for now, an if things pick up they will bring me back. they said I could claim up to 99 weeks of unemployment and I needed to go ahead and file and enjoy my time off. They said this was only temporary. They brought in a guy approx 6 weeks before I left and had me train him on every detail of my job. They said he will be filling in for me while I am gone. Legally can they lay me off and give him my position? Any feed back is appreciated! Thank you!