Worcester-based Webster First Federal Credit Union got the green light Tuesday 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 Tuesday, and the merger is expected to be made official Saturday, Webster First said in a statement.

Webster First has been an aggressive merger-seeker 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.

Seventy-eight-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.

It also gets Webster First quick access to the Boston market.

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

"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," said Edward Mahan, Filene Federal’s president and CEO, in prepared remarks.

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