Kirkland & Ellis refused to allow Hong Kong M&A partner Frank Sun to leave for Latham & Watkins until he repaid a $120,000 (£83,000) bonus.

Legal Week understands Sun was forced to pay back the bonus personally before he left last month for Latham, with Latham subsequently reimbursing him in full.

Sun received the bonus at the end of 2014 as a loan that was to be repaid if he left Kirkland within two years.

Latham was aware of the condition on the bonus when it hired Sun from its US rival but is thought to have assumed Kirkland would waive the obligation.

Many firms have conditions associated with partner departures but it is less common for those leaving to be held to the terms in full, according to those in the market.

One partner with knowledge of the matter said: "It is the same as the way magic circle firms put in gardening leave provisions for a year but they rarely enforce the full 12 months.

"This is a big, powerful firm – are they so desperate they can't let a young partner leave without him paying back a bonus he got in 2014?"

Another partner in Hong Kong said: "We would never think about paying a partner a bonus with a string on it."

Last year, Kirkland had a total of 351 equity partners globally, with profit per partner rising 2.7% to $3.6m. Latham had 454 equity partners in 2015 with profit per partner standing at $2.9m.

In March, Legal Week revealed Kirkland had doubled its notice period for departing partners worldwide from 60 days to 120 days.

The firm, which saw seven London partners hand in their notice in the same month and has seen dozens leave around the world during the past two years, has also introduced a 30-day notice period for its large-salaried partner rank.

Previously, salaried partners were not held to a notice period or put on gardening leave.

Kirkland and Latham declined to comment.