There's no law that says that an employer can't require a high school diploma.
Most employers will want an employee to hold a high school diploma or GED before even considering the employee for the job.
So it's very important to have a high school diploma or GED to get a Job but you may be able to find some types of jobs such as online jobs or some other manual labor jobs that don't require a GED.
You could start your own business too and be your own boss such as in a landscaping or other type of business or even work from home and run an Ebay Store or design and sell T Shirts Online.
You can also find type from home jobs or do freelancing to make some income online without needing a high school diploma or GED.
I have a high school diploma but lost my Job and now I do freelance work from home and I'm much happier not having to go into an office everyday or do manual labor outside and have a boss telling me what to do.
I work from home doing the freelance work and I'm my own boss and do the jobs I want to do when I want to do them.