Connecticut Attorney General William Tong assailed M&T Bank’s merging of accounts with People’s United Bank, accusing the bank of a “serious lack of preparation for this conversion” and demanding a swift resolution to more than a week of customer disruptions.

“Should Connecticut consumers continue to experience extended gaps in customer service, my office will not hesitate to use the full extent of our authority to protect families and businesses,” Tong wrote to Buffalo-based M&T in a letter dated Wednesday.

Tong noted that customers have been blocked from online accounts and phone apps; wait times in branches and on the phone has been unacceptably long; real estate closings may have been delayed and otherwise complicated; and automatic payments have been disrupted, among other complaints.

Tong pushed for a meeting with a high-level executive after his office fielded numerous complaints from customers and employees following the account conversion over the Labor Day holiday weekend.

In his letter to Mike Keegan, M&T’s chief of community markets, Tong said his confidence in M&T’s acquisition of Bridgeport-based People’s United was further shaken by the troubled account conversion, coming after last year’s confrontation with the bank over potential job losses.

The fallout over the account conversion hit particularly hard in Connecticut, where People’s United — one of the largest Connecticut-based banks — had hundreds of thousands of consumer and business customers.

Max Reiss, an M&T spokesman, said in a written statement that bank executives are willing to meet with Tong immediately to address his concerns.

“We are in complete agreement that we must remain laser-focused to serve customers and improve their experience as they interact with a new financial institution for the first time,” Reiss said. “That is why we have been open with our customers before and during the conversion process.”

Reiss said the vast majority of customers have successfully come on board with the bank, but “we know the experience for others have fallen short of our expectations.”

Reiss said the bank has beefed up staff in branches to help customers with the transition; worked on reducing wait times on customer service lines and reached out to customers to activate cards and accounts.

In addition to the tumultuous account conversion, Tong took aim at the combination of the workforces of the two banks.

M&T pledged in August, 2021 to employ at least 1,000 within a year at the Bridgeport headquarters of People’s United Bank after closing its acquisition of People’s United and combining account systems.

M&T made that commitment in a letter to Tong, who along with a growing number of local, state and federal elected officials, expressed alarm at the depth of the job cuts disclosed by M&T in filing the previous month.

The labor department filing disclosed that 747 jobs — 661 of them at the People’s United’s Main Street headquarters — were on the chopping block. Elected officials said they were taken off guard, having understood job loss would be minimal.

Tong praised the agreement in 2021, but said he would be monitoring the combination of the two banks.

In his letter Tuesday, Tong said he was disturbed by reports from former People’s United employees who have been technically “retained” but in jobs with significantly less pay.

Employees have complained that jobs have been “siphoned off” from elsewhere in the state to meet the Bridgeport employment requirements, Tong said.

Employees also have said the majority of new job openings are in New York and not Connecticut.

In his letter, Tong asked for an accounting of how many employees who were among the initial 747 had, so far, lost their jobs.

Kenneth R. Gosselin can be reached at kgosselin@courant.com.