Nikki Fried, a Democrat running for agriculture commissioner in Florida, has made no secret of her support for medical marijuana.

Further expansion of the state's program is the highest priority on her campaign website. Before entering the race, she ran a lobbying firm, Igniting Florida, and described herself as "one of most visible faces and key activists in Florida's burgeoning medical cannabis industry."

Even so, employees at Wells Fargo, where her campaign held an account, had questions about her platform.

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The bank, which says it has a policy against serving marijuana-related businesses, had noticed that Ms. Fried was "advocating for expanded patient access to medical marijuana." It asked the campaign in July whether it would be receiving money from "lobbyists from the medical marijuana industry in any capacity."

The campaign replied that, yes, Ms. Fried would be receiving donations from lobbyists as well as "executives, employees and corporations in the medical marijuana industry."

Last week, the campaign said it had received written notice that Wells Fargo was closing its account.

On Monday, Ms. Fried urged her supporters to consider pulling their money from the bank.

"This is absolutely unprecedented," she said in a telephone interview. "I've been in this campaign since the beginning of June. Everybody in Florida knows that I'm one of the main proponents of the expansion of medical marijuana."

Wells Fargo isn't the first bank to close a customer's account over money that could be related to the sale of marijuana, which is legal in some form in states including Florida but still prohibited by federal law.

That conflict has had banks large and small walking a line for more than a decade, since the first states began changing their cannabis laws. Marijuana growers have struggled to open and maintain bank accounts, and dispensaries have relied on cash to do business instead of credit cards. Businesses like construction companies and electricians that provide services to the growers and distributors have also had problems.

The biggest banks are traditionally the most cautious. But Wells Fargo's scrutiny of Ms. Fried's political beliefs set its decision apart.

"If a bank is going to start drawing a line based on a candidate's particular advocacy, where does a bank draw that line?" asked Christian Bax, who until Aug. 10 was Florida's medical marijuana director. "Is it going to extend to every candidate in Florida who advocates for medical marijuana?"

A Wells Fargo spokeswoman declined to discuss Ms. Fried's case specifically, but said the bank has a policy of avoiding the marijuana industry.

"It is Wells Fargo's policy not to knowingly bank or provide services to marijuana businesses or for activities related to those businesses, based on federal laws under which the sale and use of marijuana is illegal even if state laws differ," the spokeswoman, Bridget Braxton, said in a statement. "We continually review our banking relationships to ensure we adhere to strict regulatory and risk guidelines."

Erik Gordon, assistant professor at University of Michigan's Ross School of Business, said that while it was highly unlikely that Ms. Fried could successfully claim Wells Fargo had impeded her right to free speech, the bank's move seemed to him "like semi-paranoid overkill."

"They're seeing the word 'marijuana' — they're seeing a word that could indicate danger — and are assuming that the danger exists without thinking carefully about what's going on," he said.

Banks have gotten mixed signals about marijuana from the federal government. In 2013, the Justice Department announced that it would not commit resources to prosecuting legitimate marijuana businesses and would instead focus on things like breaking up drug-trafficking rings and preventing the sale of marijuana to children. But the Trump administration rescinded that guidance in January, saying prosecutors should use their discretion to prosecute marijuana-related cases just as they would for any other category of offenses.

Banks generally take their cue from the Treasury Department's Financial Crimes Enforcement Network, which, in 2014, offered a checklist of things to watch for when providing banking services to legal marijuana businesses, with an eye toward ensuring that banks don't end up accidentally providing services to criminals.

Wells Fargo's regulator, the Office of the Comptroller of the Currency, said it did not encourage or discourage banks from providing services to specific industries.

"We expect banks to assess the risks posed by individual customers on a case-by-case basis and to implement appropriate controls to manage their relationships," said Bryan Hubbard, a spokesman for the agency.

Florida began in 2015 to put together a framework for giving patients, including people with chronic pain and post-traumatic stress disorder, access to medical marijuana. More than a dozen businesses are licensed to provide medical marijuana in the state, and around 120,000 people have cards that give them access to the drug.

But some advocates, including Ms. Fried, say the state isn't moving fast enough to expand access, and four Democratic candidates for governor have advocated decriminalization or legalization of recreational marijuana in some form.

Democrats and Republicans alike are getting the support of the marijuana industry. For example, one Florida marijuana grower, Surterra Holdings, gave $25,000 to the Florida Republican Senatorial Campaign this year. Surterra also donated to four current Republican state representatives.

Bank lobbyists say it's up to Congress to offer guidance.

"This is symptomatic of the confusion created by conflicts between state and federal law on marijuana-related issues, and banks have no clear rules of the road," said Jeff Sigmund, a spokesman for the American Bankers Association.

But in closing a campaign account, Wells stands alone. Representatives for Bank of America, Citigroup and JPMorgan Chase said their banks did not have policies that would prevent them from offering services to a candidate like Ms. Fried.

Neither, it seems, does BB&T, which now maintains Ms. Fried's campaign account.