The owners of 400 Atlantic St. want to restructure the tower’s debt. CoStar

The weak Stamford, Conn., office leasing market is creating a headache for a high-profile building operated by Landis Group, a company founded by one of the owners of the Minnesota Vikings.

The owner of the office building at 400 Atlantic St. has informed the servicer of a $265 million mortgage backed by the 527,000-square-foot tower that it wants to restructure the debt, according to Trepp LLC, which tracks commercial real estate bonds. The owner cited a wide range of problems including Stamford’s high vacancy rate and the likelihood that the building’s major tenants won’t extend their leases when they expire in a few years, Trepp said.

“This loan will very likely be transferred to the special servicer next month,” Trepp said in its report. Special servicers typically get involved in loans when they run into problems.

A spokeswoman for the building’s owner pointed out that the loan isn’t in default and that the landlord is acting prudently. “In light of the challenging market conditions, ownership has engaged the lender in advance of the loan maturity as a prudent and proactive step toward stabilizing the building on a long-term basis,” she said in an email.

The big tenants that are likely giving up some or all of their space include UBS AG , which leases about half the building and has been consolidating its operations. Also International Paper, which has about one quarter of the space, announced plans to relocate its headquarters from Stamford to Memphis about one decade ago and is mostly moved out.

The building is owned by a venture led by Landis, a real-estate investment company founded by Alan Landis, a well-known developer who is a Vikings ownership partner. Landis Group is being run these days by his son, Scott Landis.

The problems facing 400 Atlantic underscore several major trends sweeping the region’s office markets. One is that Manhattan is doing much better than the surrounding regions thanks in part to the growing appeal of the urban lifestyle to young and talented workers.

At the end of the second quarter, the office vacancy was 11% in Midtown Manhattan; 10% downtown and 8.2% in Midtown South, according to Cushman & Wakefield. By comparison, the vacancy rate was 27.9% in downtown Stamford, Cushman & Wakefield said.

The other problem hurting Stamford is the consolidation of the financial services industry, which long has been an engine of growth in the region. In Manhattan, slowing demand from securities firms and banks has been eased by the growth of its technology sector. But suburban markets have been more vulnerable to the contraction because they don’t have as many new and expanding businesses.

UBS has been closely watched in both Manhattan and Stamford because of the high-profile deal cut by one of its predecessor firms, Swiss Bank Corp., to relocate about 2,000 employees from Manhattan to a new downtown Stamford complex with a trading floor that the company said was the largest in the world. That building was at 677 Washington Blvd.

But in recent years, UBS, which was formed by the 1998 merger of Union Bank of Switzerland and Swiss Bank, has been trimming its trading and investment banking operations. The football-field-sized trading room at 677 Washington has been occupied these days mostly by back-office, legal and technology staffers, according to people familiar with the bank.

UBS in 2011 again made headlines by considering the possibility of moving Stamford operations back to Manhattan. But the firm made a commitment to keep the jobs in Stamford for at least five years.

Since then UBS has been consolidating its Stamford operations, though, moving people from 400 Atlantic to 677 Washington. Its lease at 400 Atlantic ends in 2015, according to Trepp.

A UBS spokeswoman said in an email that the firm “has repeatedly stated its commitment to maintaining a presence in Stamford and keeping at least 2,000 jobs in Connecticut through 2017.”

International Paper’s lease for about 120,000 square feet at 400 Atlantic ends next year. A spokesman for the company said in an email that International Paper continues to occupy about 11,000 square feet and will continue to occupy that space.

The company has been subleasing its other space and won’t lease it again when its lease expires, the spokesman said.

Write to Peter Grant at peter.grant@wsj.com