WASHINGTON — More than 100 Republican donors — many of them prominent names in their party’s establishment — sent a letter to Republican members of Congress on Tuesday urging them to support an overhaul of the nation’s immigration laws.

The letter, which calls for “legal status” for the 11 million immigrants here illegally, begins with a simple appeal: “We write to urge you to take action to fix our broken immigration system.”

The effort was organized by Carlos Gutierrez, who was secretary of commerce under President George W. Bush and was a founder of a “super PAC,” Republicans for Immigration Reform. The letter is the beginning of a campaign to lobby Republican lawmakers in favor of a broad immigration bill as they return to their districts for the August break.

“What tends to happen during the month of August is that members go home and they go to town hall meetings and they check up on their offices in terms of phone calls and letters, and that’s where they get bombarded,” Mr. Gutierrez said in a phone interview. “So Republicans who are for immigration reform — and I believe there are many — we need to make our voice known in August.”