Worcester-based Webster First Federal Credit Union got the green light last week for its fourth merger in the past year, this time with tiny Filene Federal Credit Union in Boston.

Filene Federal’s members voted to approve the merger last Tuesday, and it was expected to be made official Saturday, according to Webster First.

Webster First has been an opportunistic merger-maker recently. In the last year, it has acquired Saugus Federal Credit Union, Fitchburg Federal Credit Union and Winthrop Federal Credit Union, bringing its total assets to $619 million.

The acquisition of 78-year-old Filene Federal, with 1,700 members, $20 million in assets and a single branch on Tremont Street in Boston, brings Webster First to about $639 million in assets and about 50,000 members.

The Saugus and Winthrop acquisitions brought Webster to Boston’s borders, but the latest acquisition gives Webster First quick access to Boston proper.

“Tremont Street is a great location with a lot of potential,” Webster First President and CEO Michael Lussier said in a statement.

He said the credit unions Webster First has acquired keep all their employees, and even their names. They operate as “a division of” Webster First, and add that verbiage to their signs, he said.

“These institutions are successful institutions,” Lussier told Banker & Tradesman. “Some of them have been in the community since 1920, but they need some help. The narrowed interest margins and the constant increases in regulations and compliance issues is making it difficult.”

Filene Federal was connected with the now defunct Filene’s department store. Filene’s Basement closed in December after an earlier bankruptcy sale.

“This merger makes both credit unions, Filene and Webster First, financially stronger, especially through this economy. I am excited to call Webster First Federal Credit Union and Filene partners in this strategic merger,” Edward Mahan, Filene Federal’s president and CEO, said in prepared remarks.

The National Credit Union Administration approved the transaction earlier this year.

More Than Mergers 

Mergers aren’t the only item, however, in Webster First’s growth strategy. Lussier told Banker & Tradesman that Webster First intends to open a new branch over the summer in Hopkinton.

Lussier said in the year that it has closed four mergers, 17-branch Webster First has also grown about $10 million in deposits, thanks to customers “upset with the typical big bank.”

“Many of the people upset with the typical big bank are coming to a credit union, and some are coming to us,” Lussier said.

It’s already been an interesting year for Massachusetts credit unions.

In late March, HarborOne Credit Union’s board of directors unanimously approved a plan to pursue a conversion to a mutual cooperative bank charter. The $1.8 billion credit union, one of the state’s largest, says becoming a bank will allow it to pursue customers into Boston and beyond.

Also, Gardner-based GFA Credit Union, which by assets is a bit more than half the size of Webster First, is acquiring Monadnock Community Bank, of Peterborough, N.H. The failing, $82 million, one-branch institution was ordered by regulators to seek out a merger or acquisition partner.

Webster First, which has about 208 employees, isn’t on the prowl for acquisitions, but tends to be decisive when opportunities arise, Lussier said.