“You’re either going to be at the table, or you’re going to be on the table,” said Thomas M. Reynolds, a former Republican congressman from New York who served on the tax-writing Ways and Means Committee and is now a lobbyist at Holland & Knight focusing on tax issues. Most businesses that could be affected by the tax overhaul “will not have to be encouraged to engage,” Mr. Reynolds said.

“Everybody is beginning to pay attention, and there is going to be a flurry of people looking for representation,” he added.

The spike in tax-related lobbying is already well underway, prompted by Mr. Trump’s campaign-trail pledge that fundamentally overhauling the tax code would be one of his top priorities in the White House. Companies and trade associations have submitted nearly 450 filings to lobby on tax issues from the beginning of the year through the end of last week, compared with fewer than 265 filings for all of 2016, according to congressional lobbying disclosures.

There is some irony in Mr. Trump’s setting off a surge in lobbying spending, given his campaign promise to “drain the swamp” in the nation’s capital, partly by taking on special interests. But there is perhaps no federal law that has been lobbied as assiduously as the tax code. Its thousands of pages contain countless provisions inserted at the behest of specific groups that have an interest in protecting their benefits.

“People have been expecting this all year. But the feeling that specific provisions could be put in play is now more real, and all of those provisions have a constituency and a lobbyist,” said Randolf H. Hardock, a tax lobbyist at Davis & Harman. “Some of it is just keeping clients informed, even if they don’t ultimately engage, because there are issues that could come up right at the end, where if you’re not paying attention, you could miss them.”