Bank of Montreal said on Friday it is suing four of its former bankers and the bank they are joining, UBS AG, in a bid to retrieve what they allege was confidential information the bankers took with them before resigning.

Last week, UBS poached a U.S. team of 15 oil and gas bankers from BMO in Houston, Texas, weakening the energy dealmaking capacity of Canada's fourth-largest bank in the heart of the U.S. oil and gas industry.

In a suit filed in the U.S. District Court for the Southern District of Texas, BMO sought a preliminary injunction to force the bankers - Miles Redfield, David Edwards, Robin Gaines and Justin Colby - to return what it said was the confidential information that was taken or retained by them before their departure.

BMO is seeking to prevent the bankers named from disclosing any of this information and stop them from contacting or wooing BMO's clients.

A spokeswoman for UBS declined to comment on the matter. The four bankers could not immediately be reached for comment.

BMO is also asking the court to order the bankers to preserve electronic evidence and allow for forensic imaging of computers, tablets, and mobile devices that they own.

The lawsuit is in support of an arbitration process BMO is pursuing against UBS and the four bankers before the Financial Industry Regulatory Authority (FINRA), BMO said.

The team of bankers that left BMO were part of a specialist group dubbed Acquisitions & Divestitures. This team carried out the complex engineering and technical research needed to value oil and gas deposits far beneath the Earth's surface.

The team was led by Redfield, who sources last week told Reuters, is now set to take on a senior role at UBS.

A source familiar with the situation said on Friday that the majority of the bankers, who departed BMO are in fairly junior roles, with only three, or four in senior client-facing roles.

The suit is No: 4:15-cv-00723 in the Houston Division of the U.S. District Court for the Southern District of Texas.