Industries from around the world spent nearly $1 billion to lobby the federal government during the first quarter of this year, according to a new analysis by the Center for Responsive Politics — the highest in five years.

The uptick was driven by both optimism and fear over the priorities of President Trump and the Republican Congress, lobbying experts said. However, nervous drugmakers logged their biggest increase in spending amid signs that the new president may try to drive down drug prices.

“The first 100 days of the Trump administration have been extremely chaotic,” said Muftiah M. McCartin, a vice chair at Covington & Burling, which saw a 32 percent spike in earnings from lobbying, the largest growth of any firm. “As a result, companies across the globe are seeking assistance to help navigate the new administration.”

As president, Trump has vowed to pursue sweeping policies that would have an enormous impact on a wide range of industries, including eliminating 75 percent of federal regulations and overhauling the federal tax code. Congressional Republicans, who secured full control of the Capitol in the 2016 election, are already at work trying to fulfill another Trump pledge: rewriting health reforms enacted in the 2010 Affordable Care Act.

While first-quarter spending on lobbying grew to $838 million from $827 million during the same period last year, the number of registered lobbyists actually declined to 9,175 from 10,225. Lobbying experts said the decline was due in part to Trump’s announcement that lobbyists would not be welcome on his transition team or in his administration.

The administration since has relaxed that position, but lobbying experts said they expect the trend to hold.

“I think Trump has made it clear that being a lobbyist is not something that is held in high regard,” said Caleb P. Burns, a partner at Wiley Rein, which has seen its lobbying earnings drop slightly in the first part of this year. “I don’t think that has materially changed, and I predict those numbers won’t rise.”

Spending, on the other hand, is rising rapidly. Covington, the biggest beneficiary, earned $4 million during the first part of this year. Donations by the firm’s political action committee heavily favored Republican candidates last year, according to a CRP analysis. The firm has been hired to work on numerous issues, including trade, health care, food and drug safety, national security, transportation and infrastructure, and tax reform.

The biggest jump in spending came from the Pharmaceutical Research and Manufacturers of America (PhRMA), the drug industry’s trade group, which spent $8 million during the first quarter of the year, a 35 percent increase over the first quarter of 2016. PhRMA was the third-highest spender in the first quarter, the center’s analysis showed, moving up from No. 5 during the same period in 2016.

A PhRMA spokesman said the group does not comment on lobbying activity. However, drugmakers have expressed concerns about a number of issues since Trump was elected.

In a Fox News interview in February, for example, Trump said he would look for ways to lower drug prices, stating, “My new thing is going to be pharma, because we pay too much.” Trump also spoke in support of permitting Medicare — the nation’s largest purchaser of prescription drugs — to negotiate with drugmakers to drive down costs, an idea the industry has long opposed.

Drugmakers also have been alarmed by Trump’s interest in speeding up the rigorous federal drug-approval process. Drugmakers consider federal testing and review critical to building confidence in new — and often expensive — medications. In contrast to many other industries, PhRMA has hired lobbyists to keep the current regulatory system in place.

The U.S. Chamber of Commerce continues to rank first in spending, significantly outpacing every other company, industry and trade group, the analysis shows. The Chamber spent nearly $25 million — an 8 percent increase over the first quarter of last year and more than double the amount spent by the second-ranking National Association of Realtors, the analysis showed.

Chamber spokeswoman Blair Latoff Holmes said “the Chamber’s lobbying activity reflected our commitment to advancing regulatory reform and cutting red tape.” Holmes said the group’s top legislative priorities include the Regulatory Accountability Act, which would significantly restrict the federal government’s power to adopt new regulations or safety standards. The bill has passed the House but has yet to be taken up in the Senate.

AT&T also ranked near the top in lobbying spending in the first quarter of this year, reporting nearly $4.6 million in lobbying costs. In February, the company paid $85.4 billion to acquire Time Warner, a deal that will not be finalized unless federal antitrust officials determine it would hurt not consumers.

During the campaign, Trump expressed opposition to the deal, saying it would put “too much concentration of power in the hands of too few.” Democrats in Congress also have raised concerns about the deal, which is under review by the Justice Department.

Alice Crites contributed to this report.