Is it legal for a H1B holder to work under 2 employers at a time

Will it be a problem if an H1B holder has worked under two different employers at a time for a short period of 1 week?
I need this information in order to apply for my visa extension. And would like to know if this overlap period will cause any legal issue for my visa extension.
Can someone help me with this query ASAP.

It is not allowed to work for 2 different employers full time. If you had concurrent h1 then it is possible but not without that. Why is this important for extension btw ?

I don’t it will cause an issue w/ H-1 extension.