SOUTH LAKE TAHOE. (AP) — U.S. Sens. Harry Reid and Dianne Feinstein urged the Sierra Club not to delay implementation of a new plan to guide future development at Lake Tahoe — shortly before the environmental group sued over it.

Reid, D-Nev., and Feinstein, D-Calif., in a Feb. 1 letter to the Sierra Club, warned that millions of dollars in federal funding and the very existence of the bi-state Tahoe Regional Planning Agency could be jeopardized by delays in implementing the agency's new regional plan.

The Sierra Club and Friends of the West Shore filed a lawsuit Monday in U.S. District Court in Sacramento. The group claimed the rules that the agency adopted in December will erode environmental protection of the mountain lake by allowing denser development and giving more control to local governments.

Reid and Feinstein urged the Sierra Club to "refrain from any actions that might result in the dissolution of the bi-state compact or set back our efforts to pass legislation to help restore lake clarity."

"The adoption of the plan is the result of nearly a decade of work by TRPA, local government, residents, business owners and environmental groups and takes into account more than 5,000 public comments," the senators wrote in the letter obtained by the Tahoe Daily Tribune (http://bit.ly/XawpmG ).

"The plan reflects policy compromises of this diverse group of stakeholders with the overarching goal of restoring Lake Tahoe's world-famous clarity while at the same time supporting desperately needed revitalization."

Bruce Hamilton, deputy executive director of the Sierra Club, said his group had hoped to extend the deadline for a lawsuit in order to further negotiate with the agency.

"We agreed with the senators that it was far better to work out a better plan than to litigate, so we made a good faith effort to get TRPA to agree to extend the deadline to sue in order to facilitate negotiations in the hope of avoiding a suit — but they refused," Hamilton told the Tribune. "That refusal left us with the choice of either letting a terrible plan that won't protect the lake go forward unchallenged or to proceed with the litigation. For the sake of Lake Tahoe, a national treasure, and all Americans who enjoy the lake's pristine clarity, we chose the latter."

Reid and Feinstein warned that any delay in implementing the new regional plan could jeopardize the compact between California and Nevada that established the agency in 1969. The regulatory agency is charged with overseeing development at the lake.

Clashes between Nevada and California over development in the Tahoe Basin prompted Nevada lawmakers in 2011 to pass a bill that paved the way for Nevada to pull out of the compact in 2015 unless the regional plan was updated to give more consideration to economic factors.

Some Nevada members of TRPA's governing board have said they would support legislation to rescind the law this year if the plan wasn't challenged in court.

"This compact ... is vital to the preservation of Lake Tahoe," Reid and Feinstein wrote. "If either state were to withdraw from the compact, as proposed under existing Nevada state law, the decades-long investment we have collectively made in Lake Tahoe's restoration would be undermined."

Representatives of Reid and Feinstein did not immediately respond to requests for comment.