Tech investors — including Dallas Mavericks owner Mark Cuban, the co-founder of Reddit and the co-founder of AOL — are asking Congress to pass broad patent reform.

In a letter to Congress on Wednesday, the group of 39 tech investors warned of the harms of patent trolls, which they said cost companies $29 billion in 2011.

{mosads}The letter was sent by patent reform advocacy groups the Electronic Frontier Foundation, the Application Developer’s Alliance and Engine Advocacy.

“We write to urge comprehensive legislation to address the troubling growth and success of the patent troll business model,” which depends on threatening litigation often using vague claims of patent infringement, the group of investors wrote.

“Young, innovative companies are increasingly threatened and targeted by patent troll lawsuits.”

To solve the problem of patent trolls, Congress needs comprehensive reform that makes “it harder to be a patent troll, and easier for targeted businesses to protect and defend themselves,” they said.

The investors asked that broad reform include transparency requirements from the companies making accusations of patent infringement, limits on the burdens that can be placed on the companies being sued and an easier way to challenge patents at the U.S. Patent and Trademark Office.

The investors who signed the letter include leaders of venture capital firms that back tech companies of all sizes, including Facebook, Twitter and Netflix.

“We are the fuel in America’s startup economy engine,” they wrote.