Subway is clashing with its franchisees over the fast-food chain’s plans for an aggressive “Buy a footlong and get a footlong” sandwich promotion, The Post has learned.

The upcoming deal — which will be available nationwide from March 5 to April 15 — will be available to customers who order online or use Subway’s mobile app, according to sources familiar with the plans.

The idea is to boost Subway’s online and mobile-based business, which currently accounts for just 1.4 percent of the total, the Subway Franchisee Advertising Trust Fund said earlier this week in response to questions on a franchisee site.

Subway’s goal is to get that number to 5 percent, the company said.

“Is there going to be any compensation from Subway to the franchisees for the loss they are going to incur with this promotion — after all the franchisee is giving a footlong free for every footlong?” Nayanika Barker, chair of the National Association of Subway Franchisees, asked Subway in a back-and-forth exchange on the site.

“No, similar to other offers, there is no additional compensation,” Subway answered, according to a screenshot reviewed by The Post.

Many of Subway’s restaurants are already losing money. More than 1,100 closed on a net basis in both 2018 and 2019, leaving about 23,600.

John Chidsey, who became CEO in November, seized control of 95 percent of the fast-food giant’s advertising, which used to split about 40-60 between territories and headquarters.

Chidsey became notorious when running Burger King for forcing a $1 double cheeseburger promotion that store operators sold for a loss — despite having voted twice to reject the promotion. That resulted in a lawsuit that was settled after private equity group 3G Capital bought the chain in 2010.

In 2017, Subway franchisees started a petition drive to protest a $4.99 footlong promotion. Six months later, Subway CEO Suzanne Greco announced her retirement.

Subway didn’t immediately respond to requests for comment.