There aren't that many laws that can prevent drivers from denying service, I don't think. Maybe race, religion and gender?  

Lyft has a community guideline, so technically, anyone who breaks this you should be able to refuse a ride. At the least Lyft will back you up if you are following the rules mentioned here.

https://help.lyft.com/hc/en-us/articles/360000100648-Community-guidelines 

Aggressive, dirty, or drunk. Other than that, I think I take anyone. 

Here's a relevant thread:

Can Uber and Lyft drivers refuse a passenger for any reason?

Didn't you guys see this?

This is what happens if you don't get out of a car.

Basically, drivers can refuse a ride (i.e. cancel, decline, etc.) for any reasons at all as they are independent contractors driving their own private vehicles.

apparently, they still are not allowed to discriminate based on gender, religion, or race.  and if the rider has a service animal.

I once refused service to two naked dudes in roller blades.  

Where? Manhattan Beach, of course.

I believe they can refuse if they feel they will be put in an unsafe situation. This would include taking passengers who are rowdy, violent, or too drunk.

They can also refuse minors, those with pets that are not service animals, and those who have twoo many passengers for their car.

Technically, any circumstances. We are not required to take anyone. We are independent contractors and no one can tell us what to do. (though, maybe not in CA anymore.)

I am not sure even if race, gender and religion can stop us from cherry picking rides.