SAN FRANCISCO—After enjoying a wildly successful 2014, the ride-sharing application Uber has begun to experiment with taking up to 30% commission from new drivers.

The pilot program, taking place in San Francisco, will take a 30% commission from new drivers’ first 20 rides per week, decreasing the percentage to 25% for the 20 subsequent rides, and 20% for all rides after that.

The company is also trying a similar program in San Diego, with the lone difference being that the percentage decreases take place every 15 rides.

The pilot program will most severely effect UberX drivers who work only a few hours per week. Though 20% used to be the standard commission for all UberX drivers, few working for the company part-time will ever reach that number.

Full-time drivers will also be severely effected, but should be able to reach the top level of the commission hierarchy by week’s end.

Uber, which is reportedly nearing a valuation of $50 billion, has asserted that drivers who joined before April will not be affected.