PROVIDENCE — A third online retailer has severed its relationships with marketing partners based in Rhode Island amid a growing battle over the state’s plan to expand its collection of sales tax on online purchases.

Blue Nile Inc., a Seattle-based jewelry retailer, informed Rhode Island Web site publishers on Tuesday that it was immediately ending its affiliate program here, which allows them to earn sales commissions by posting links to Blue Nile product pages, TechFlash reported.

“Blue Nile regrets the need to take this action,” the company said in an e-mail to affiliates obtained by TechFlash. The message added: “We remain hopeful that this unconstitutional legislation will eventually be repealed, at which point we would be happy to resume working together.”

Amazon.com, which is also based in Seattle, and Salt Lake City-based Overstock.com also cut off their affiliates in Rhode Island this week over the new law. Affiliate programs also have been ended in North Carolina, Hawaii and California, although Overstock reinstated it in the latter state after Gov. Arnold Schwarzenegger vetoed the offending legislation.

The e-retailers are contesting a provision in the state budget signed into law earlier this week by Gov. Donald L. Carcieri that requires them to collect taxes on purchases made through the site of a Rhode Island-based author or company.

A Supreme Court decision most recently affirmed in 1992 said that companies cannot be forced to collect sales tax unless they have a “physical presence” in the state. Lawmakers argue the affiliates constitute a physical presence, which the retailers contest.

In Rhode Island, not having to charge sales tax effectively makes a book or other product 7 percent cheaper to buy on Amazon.com than it would be in, say, a brick-and-mortar Borders store. Larry Dignan, a longtime tech industry observer, wrote on CNET earlier this week that Amazon “is likely to come out a winner” on the sales tax dispute.

“Think about it: If Amazon was really dependent on the [affiliates] program for a huge portion of sales would it really just pull it that quickly?” Dignan wrote. He added: “It’s hard to quantify the connection between referrals and Amazon’s sales, but chances are good that the company has word of mouth, habits and low prices at its back these days.”

Imran Khan, an analyst at JPMorgan Chase, made a similar point in a research note quoted by Dignan. “Although the affiliate network changes could result in some lost sales, Amazon will have the ability to shift marketing spend into other arenas,” Khan said. “We think the company can continue to focus its marketing on the areas that deliver the best (return on investment), mitigating the impact of losing some affiliates.”