(Reuters) - After voters in four states on Nov. 3 passed measures legalizing the recreational use of marijuana, lawyers who focus on representing cannabis-related clients are feeling, well, high about the future of the practice area.

I had a chance to talk with some of the original Big Law cannabis pioneers about what they see ahead, including a shared expectation that more major firms will soon start competing with them for the business.

"I do anticipate the proliferation of cannabis-related work among the bigger law firms," said Jonathan Robbins, who in 2014 launched Akerman's 30-plus lawyer cannabis practice. But he also has a warning: "These are not easy waters to navigate."

New Jersey, Arizona, Montana and South Dakota are the most recent states to greenlight the adult use of recreational marijuana, which is also legal in 11 other states plus the District of Columbia. In addition, Mississippi voters just approved a measure allowing doctors to prescribe medical marijuana.

Lawyers are especially bullish about New Jersey. With its proximity to New York, Connecticut and Pennsylvania, it's poised to become the biggest cannabis market in the U.S. other than California, they said. (California in 2019 had nearly $3.9 billion in cannabis sales, according to Marijuana Business Daily.)

But before that happens, players across the industry are likely to need legal help on a wide range of issues.

Fox Rothschild cannabis practice co-chairs William Bogot and Joshua Horn told me they're already getting calls from clients, including a New Jersey strip mall owner considering a marijuana dispensary as a tenant and an investor group looking to enter the Garden State's cannabis market. Another firm partner who is active politically is busy sussing out New Jersey municipalities that will be receptive to cannabis businesses.

"What we do in cannabis is what any other firm would do (representing clients) in the widget business," Horn said, noting that the five-year-old practice group has grown to include 70 lawyers firm-wide.

Of course, marijuana remains illegal under federal law, which is one reason many top firms have hesitated to go after the business. But as more states legalize weed - the governors of New York and Virginia have both said they anticipate legislation moving forward next year - lawyers predict the competitive landscape will change.

"Larger firms that wouldn't touch the practice are now seeing the money and the size of the deals," Bogot said, noting that he and Horn were regulatory counsel in a $900 million transaction that closed this summer. Curaleaf Holdings Inc bought their client GR Companies Inc in a merger that created the world's largest cannabis company by revenue.

It may not be easy for newcomers to parachute in and simply declare themselves cannabis lawyers though.

"Cannabis raises some complex regulatory issues," said Seth Goldberg, who leads the 50-lawyer cannabis practice at Duane Morris. Conflicts between federal and state laws "pervade just about every cannabis-related transaction or matter."

"One of the nice things about doing this work for a number of years is you know where those issues are and how to resolve them," he added. "A discerning client would know if their cannabis counsel had the bona fides."

At the same time, Goldberg acknowledged that the industry is still very new. "One challenge for law firms is that there are no institutional clients, with relationships that span years and years," he said. In such an emerging market with rapid consolidation and exits, he said, a firm is "lucky" to have a cannabis client that lasts several years.

Still, there's plenty of work that doesn't involve "plant-touching" entities, notes Seyfarth Shaw senior counsel Stanley Jutkowitz.

His firm has offered advice to long-term clients wondering, say, how to handle an employee who tests positive on a drug test in a state where marijuana is legal. They've also provided risk analysis and other advice to clients such as accountants, packaged goods makers and real estate companies about working with cannabis growers or distributors.

While Jutkowitz and other practitioners don't expect outright legalization on the federal level any time soon, they are optimistic that the U.S. Department of Justice under President-elect Joe Biden will not crack down on marijuana-related businesses in states where recreational use is legal. Biden has also said he supports decriminalization of marijuana.

Further reform, such as passage of the SAFE Banking Act, which would shield depository institutions from being penalized by federal banking regulators for providing banking services to a legitimate marijuana- or hemp-related business, likely hinges on Democrats taking control of the U.S. Senate. The House passed the banking bill last year.

In the meantime, lawyers expect more states will continue to legalize weed — if for no other reason than cannabis is a source of jobs and revenue at a time when both are in short supply.

"Cannabis — excuse the pun — is a growing industry," Jutkowitz said. "A lot more lawyers and big law firms will be moving into the industry, but at the same time, the client base is expanding."