"It (the deal) will not result in a green light for U.S. companies in most cases to resume business in Iran," said William McGlone, a lawyer who specializes in export controls and sanctions at Latham and Watkins in Washington.
"Democrats as well as Republicans are still very strongly in favor of maintaining primary sanctions against Iran on the Hill for various reasons, and it's hard to see that dynamic changing in the near term."
McGlone said he spoke on Tuesday with a Fortune 50 company executive who wanted to know if it could resume foreign subsidiary dealings with Iran in place prior to 2012. Several other sanctions lawyers told Reuters they spent much of Tuesday answering Iran-related queries from clients.
Even if allowed, companies are likely to be wary of rushing into Iran due to concerns the policy could be reversed if a Republican wins the presidency in 2016. At least three Republican candidates said on Tuesday they would do so.
Pro-business groups have been treading carefully on Capitol Hill amid strong Republican opposition to the deal.
Republicans in Congress have long been working to sink an agreement, and several dismissed concerns that U.S. businesses would be disadvantaged in a post-deal environment.
"I think we are a long way from that," said Republican Senator John Cornyn, in response to a question about U.S. firms operating in Iran.
Some of the most influential business lobby groups have been largely muted on Iran, in contrast to their more active role in pressing for an easing of sanctions against Cuba and Russia.
Business Roundtable, made up of chief executives of the largest U.S. firms, including Boeing and Exxon Mobil Corp. , told Reuters they have not been involved in the Iran issue. The Chamber of Commerce, National Association of Manufacturers, and National Retail Federation did not respond to requests for comment.
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