Herbert Smith has issued a cash call to its equity partners, of up to £20m, ahead of its full financial merger with legacy Australian firm Freehills.

The outfit, whose partnership with Freehills went live on October 1 last year, has asked its equity partners to pay £2,000 per equity point into the firm, in a bid to improve its capital structure.

Details of the capital raising were sent to partners in an email earlier this month and will not affect salaried partners or anyone on the Freehills side.

Herbert Smith currently operates an eight-year lockstep for equity partners running from 43 to 100 points, with partners moving up seven points in all but the final year, when they jump eight points.

Based on numbers provided by legacy Herbert Smith for last year's UK  top 50 rankings, the firm had 270 partners during the 2011-12 financial year of which 131 were full equity. Sixty-nine of these sat at the top of the lockstep and would therefore have to pay in £200,000 each, coming to a total of nearly £14m.

Commenting on the cash call, one former Herbert Smith partner said: "I would guess that this is because of a couple of things. They have been investing heavily – a lot of different practice areas wanted new offices, so energy desperately wanted Australia and Korea, litigation wanted New York, they were looking at Guinea as well. And they have also taken on some new laterals to fill some holes which is expensive.

"Also 18 months to two years ago they paid off a lot of people as part of the equity management programme – they had about 15 partners on the list for that."

Herbert Smith and Australia's Freehills completed their merger on 1 October last year, creating a new firm with 2,800 lawyers, including 460 partners across 20 offices.

The combined outfit, which is being jointly led by joint chief executives David Willis from Herbert Smith and Freehills' Gavin Bell, is expected to generate revenues of almost £800m through a full financial union.

As part of the integration Herbert Smith is considering a move to a modified lockstep in order to better align its compensation scheme with that of legacy Freehills. The legacy UK firm has also seen a string of partner exits in recent months – with its disputes arm hit particularly hard.

Currently Freehills' all-equity partnership is remunerated on a heavily modified lockstep, running from 40 to 120 points.

Herbert Smith is not the only firm to seek a cash injection from its equity partners in recent months.

In September, equity partners at Ashurst were also asked to pay additional capital into the firm via a new financial structure, as it prepares for its tie up with Australia's Blake Dawson.

Ashurst announced its partnership with Blake Dawson in September 2011. The two firms are set for a full merger in 2014.