Looking on the internet deeply has found these results:

work on a company is the most popular phrase on the web.

work at a company 119,700,000 results on the web	work on a company 14,560,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I work at a travel company. She works at a loundry company down in Granville. You work at a diaper company. we work at a company that creates video games, and I just realized there's a major glitch in one of the levels. I work at a taxi company. Next to movies, I like cars. I work at a taxi company. You know, there is still one way we can work at a scare company. She said she works at a stock company.	As long as he works for a company. I work in a company called NASA. I work for a company that sells to dentists. I work for a company that specializes in guerilla marketing. She works for a company that does a lot of business on the European exchange. Well, Dad works for a company that makes computers. I work for a company interested in keeping him out of trouble. I work for a company providing corporate intelligence and covert surveillance.

work at a company

119,700,000 results on the web

work on a company

14,560,000,000 results on the web

More popular!

I work at a travel company.
She works at a loundry company down in Granville.
You work at a diaper company.
we work at a company that creates video games, and I just realized there's a major glitch in one of the levels.
I work at a taxi company.
Next to movies, I like cars. I work at a taxi company.
You know, there is still one way we can work at a scare company.
She said she works at a stock company.

As long as he works for a company.
I work in a company called NASA.
I work for a company that sells to dentists.
I work for a company that specializes in guerilla marketing.
She works for a company that does a lot of business on the European exchange.
Well, Dad works for a company that makes computers.
I work for a company interested in keeping him out of trouble.
I work for a company providing corporate intelligence and covert surveillance.