A decade-long boom for corporate lobbyists in Washington, D.C., is showing signs of quieting down, just as tougher congressional rules threaten to muffle the multibillion-dollar industry even more next year.

The new rules mandate more detailed disclosure of lobbying activities, industry oversight by the Justice Department and penalties of up to $200,000 for violations. They will force corporations and trade groups to provide more precise spending records and to take a harder look at who’s lobbying for them.