Four of five U.S. broadband users are unaware of the speed of their connections, the Federal Communications Commission said on Tuesday.

A similar survey conducted by Abt/SRBI and Princeton Survey Research Associates International from April 19 to May 2 also found that one in six American mobile phone users have been shocked by surprise fees and charges in their monthly bills.

The FCC has increasingly focused on consumer protection issues surrounding broadband speeds and mobile phone charges, including fees associated with ending a contract early.

Speed matters, FCC Chairman Julius Genachowski said in a statement. The more broadband subscribers know about what speeds they need and what speeds they get, the more they can make the market work and push faster speeds over broadband networks.

In March, the FCC unveiled an Internet speed test tool at for consumers to clock the speed of their connection.

The FCC said it is also seeking 10,000 U.S. volunteers to participate in a scientific study to measure home broadband speed in the U.S.

Specialized hardware will be installed in the homes of volunteers to measure the performance of all the country's major Internet service providers across geographic regions and service tiers, the FCC said.

The FCC said it is partnering with SamKnows Limited, the same firm that conducted a similar test in the United Kingdom, to carry out the U.S. study.

The biggest U.S. broadband providers are Comcast Corp, Time Warner Cable Inc, AT&T Inc and Verizon Communications Inc.

(Reporting by John Poirier, Editing by Leslie Gevirtz)