Olswang has asked its partners to sign a lock-in agreement committing them to the firm's proposed merger with CMS and Nabarro, Legal Week understands.

Partners have been given until Monday (10 October) to decide whether to commit to the proposed merger with CMS and Nabarro, with those not agreeing to the lock-in set to move on before the go-live date.

Sources close to Olswang have suggested that the lock-in would be for one year from the eventual go-live date, with the the firms thought to be aiming to complete the tie-up by the start of the 2017-18 financial year.

Olswang currently has a partner notice period of nine months, which can be extended to 18 months in exceptional cases.

Partner lock-ins are common in the event of mergers between firms. When CMS merged with Scottish firm Dundas & Wilson in 2014, partners agreed to a two-year lock-in at an agreed level of pay, while Cobbetts partners were also committed to a two-year lock-in after the firm's 2013 takeover by DWF.

CMS, Olswang and Nabarro confirmed last week that they are in talks over a deal that could create a firm with combined revenue of almost £1bn, including turnover from the global CMS network.

It is understood that Olswang partners were presented with paperwork containing details of the proposed tie-up last Friday (30 September), and that the lock-in agreement effectively serves as a vote in favour of the merger.

At this stage it is not clear whether the potential merger would include Olswang's European network, and partners in Olswang offices such as Paris and Munich are understood to be examining alternatives to joining the merged firm.

Olswang has seen a number of key partners leave the firm in recent weeks, following months of speculation about the firm's future. Recent departures include restructuring head Alicia Videon, who is joining McDermott Will & Emery, and the firm's co-head of life sciences Stephen Reese, who joined Clifford Chance earlier this week.

Olswang declined to comment.

Additional reporting by Anna Ward and Rose Walker.