Berwin Leighton Paisner (BLP) could push through its proposed combination with Bryan Cave as soon as Jan. 1, 2018, according to sources close to the British firm.

Sources familiar with the matter said that BLP partners are expecting to vote on the deal in the next four weeks.

“It’s very complicated, but I would say that this is the aspirational timeline,” said one BLP partner, who requested anonymity in order to speak freely about firm matters.

BLP and Bryan Cave confirmed their tie-up talks earlier this month in a joint announcement. The two firms reportedly seeking a close form of financial integration, as referenced in their statement, one in which Bryan Cave chair Therese Pritchard said the combined firm “would be one of only a handful of global firms operating in a one-firm structure.”

Fully integrated transatlantic mergers are rare, and present significant challenges due to the different tax and accounting systems traditionally used by U.K. and U.S. firms. U.S. firms typically rely on cash accounting, where income must be received by Dec. 31 of each calendar year, while U.K. firms normally use an accrual system, counting all billings recorded during the financial year as revenue, regardless of whether clients have paid.

If the merger goes ahead, it will create a combined firm with gross revenue approaching $1 billion mark with 1,500 lawyers working in 32 offices in 12 countries. Internet domain name records show that the website www.bryancaveblp.com was registered anonymously on Oct. 12.

Any deal is subject to the resolution of conflict issues and approval by partners at both firms.

Rumors of BLP’s ongoing desire for a merger have continued to circle the firm since its talks with Greenberg Traurig ended last year. This summer, BLP denied suggestions that it had held discussions with Norton Rose Fulbright, a global legal giant that has been particularly acquisitive in 2017.

Meanwhile, Bryan Cave has been on its own quest for growth, coming close to acquiring Dickstein Shapiro in late 2015, only to see the potential deal collapse shortly after Christmas as the bulk of the latter subsequently agreed to be absorbed by Blank Rome.

BLP declined to comment about its discussions with Bryan Cave.