In choosing Mike Pence as his running mate, Donald Trump went with a champion of free markets who boosts the ticket's appeal to the Republican donor class.
But since Mr. Pence is the sitting Indiana governor, his selection may also raise complex legal questions for some Trump supporters who've managed money for the state, including the billionaires Wilbur Ross, Stephen Feinberg, and Tom Barrack.
All three run private-equity firms that are listed as vendors in the Indiana Public Retirement System's 2015 annual report. A Securities and Exchange Commission rule sets limits on contributions to political candidates who control investment decisions, either directly or indirectly.
The "pay to play" rule was put in place in 2010 after a series of scandals in which money managers were accused of trying to improperly influence state officials to win investment management business, including by arranging political contributions.
In an e-mail message on Saturday, Mr. Ross said "I will abide by the rules" and that he's currently researching the matter "to be sure that whatever I do going forward will continue to be in compliance." Representatives for Messrs. Feinberg and Barrack had no immediate comment.
The pay-to-play rules now apply to the Trump-Pence ticket, Kenneth Gross, a political-law partner at Skadden Arps Slate Meagher & Flom in Washington, said on Friday. The "draconian" measures can lead an investment firm to be barred from doing business with a state for two years, he said. In some cases, it may even apply to people who raise money for a candidate, even if they don't contribute themselves.
The picture is murkier for donations to super-PACs, which operate independently from campaigns and can accept donations of unlimited size from individuals and corporations. The rule was put in place before super-PACs rose to prominence. Lawyers disagree about whether a donor barred from making a contribution to a candidate would be able to donate to an allied super-PAC.
Mr. Ross, whose WL Ross & Co. is listed as an Indiana money manager, held a fundraiser for Trump at his Southampton, New York, vacation home earlier this month. Mr. Feinberg, the co-founder of Cerberus Capital Management, co-hosted an event in Manhattan for Trump in June, and he and his wife contributed a total of $678,800 to a Trump joint-fundraising committee.
Mr. Barrack, the founder of Colony Capital, hosted Trump's first fundraiser at his home in Santa Monica, California in May, and gave $415,000 to a committee supporting Trump's campaign and the Republican Party.
Funds run by some of Trump's other prominent backers, including Robert Mercer of Renaissance Technologies, John Paulson of Paulson & Co., and Anthony Scaramucci of Skybridge Capital, don't appear on the Indiana list.