Is the Army combat shirt authorized now?

That is something that mission dependent. But either way you should only use in a tactical environment.

I wore my ACU patrol shirt on field problems at Fort Bliss and I know several other Soldiers that wear them in the field on other installations. I believe it's the commanders call on whether you can wear them or not during field exercises.

As far I know it is authorize only in the work place while working outside or when it is hot, but the minute you leave the work site, you must put on the rest of the uniform. It is the same rule as wearing a T-shirt.