Uber moves into business travel, expensing

Ridesharing app Uber is tapping into the massive business car service market, announcing on Tuesday a plan that allows users to bill their companies directly for the service.

With Uber for Business, employers can create an account with the car service, and then subsequently invite employees to join. Managers will then have easy access to an employee's travel information.

The company also announced partnerships with American Express and spend management company Concur Solutions. American Express cardholders will earn double points on Uber rides, while companies that already use Concur to handle travel and expense payments will be able to link their accounts with Uber.

Read More Want to profit from Uber? Here's what one pro recommends

For Uber, this is another big growth opportunity. They company already is valued at $18 billion, about the size of Hertz (HTZ) and Avis (CAR) combined.

The move follows a similar one from Airbnb, which yesterday also announced a partnership with Concur and introduced its own service for business. Both start ups are trying to cash in on the fast growing market for business travel, which is expected to generate $1.2 trillion in revenue this year, according to the Global Business Travel Association.

Uber's smartphone app allows users to order cars within minutes driven by both professional and nonprofessional drivers, and is now available in more than 130 cities. Uber CEO Travis Kalanick has said in interviews that revenue is doubling every six months, and that the company is growing faster this year than last year.

Read More Uber launchescourier service in NYC

But all that growth has come at a cost: Uber is facing resistance from state regulators who want Uber drivers to adhere to the same rules and regulations for traditional taxi and limo drivers. And Uber is also facing competition from similar rideshare services such as Lyft.

Read More Pick a sidein Uber's 'Battle for YourRide'-Commentary

-By CNBC's Josh Lipton and Mark Berniker