Republicans John McCain and Tom Coburn say they're putting their colleagues on notice: They will challenge special projects that senators insert into spending bills until the practice stops.

McCain, of Arizona, and Coburn, of Oklahoma, say recent congressional scandals stem from lobbyists' ability to persuade lawmakers to designate favored projects in big spending bills, sometimes in secret.

In a letter to fellow senators, McCain and Coburn said the practice — known as earmarking — gives lobbyists too much influence and is growing worse.

"The unsavory practice of inserting such provisions at the last minute stifles debate and empowers well-heeled lobbyists at the expense of those who cannot afford access to power," they wrote.

They said they plan to challenge "future violations of Senate rules" and offer proposals that would make it harder to bury projects without vetting them in public first.

Coburn will offer one amendment for every earmark in an appropriations bill, meaning every earmark would have to be voted on, said Coburn spokesman John Hart. Coburn has also notified Senate leaders that he will try to hold up any spending bill that comes to the floor before members have had 72 hours to read it.

Leaders from both parties are promoting ethics legislation to control lobbying in the wake of corruption scandals involving lobbyist Jack Abramoff and former Rep. Duke Cunningham, R-Calif.

Abramoff has pleaded guilty to federal felony charges related to congressional influence peddling. Cunningham recently pleaded guilty to accepting bribes from defense contractors.

While some have defended earmarks as a way for lawmakers to get needed money for their districts, McCain and Coburn argue the projects should at least be made public.

"Some have merit, some don't," Hart said. "Every senator has the responsibility to bring these projects to the light of day and the best way to do it is through floor debate and floor action."

McCain, Coburn and others have long complained about such projects buried in the transportation, agriculture, defense and other big bills.

They say the problem is growing worse — from 4,126 earmarks in 1994 to 15,268 in 2005. One recent high-profile example is the $328 million "Bridge to Nowhere" for Alaska, which last year came to symbolize irresponsible government spending.

After the plan was publicized, lawmakers removed the earmarks for two Alaska bridges, sending the money to Alaska to decide how to use it.