Allen & Overy (A&O) has toughened up its bonus eligibility criteria for associates, with fee earners now required to work at minimum 85% capacity to be considered.

The magic circle firm is currently conducting its associate performance reviews, with discretionary bonuses set to be awarded in the coming weeks.

Associates were told of the beefed up criteria after A&O managing partner Wim Dejonghe wrote to associates last year saying they must retain "busyness" levels in order to be entitled to a bonus.

A&O sets a target of 1,750 chargeable hours for associates. The new guidance means they will have to charge close to 1,500 hours to be eligible. The bonuses also factor in non-chargeable work such as business development.

A&O did not comment on the figure. However, a spokesman for the firm said: "Given associate busyness levels in London, we anticipate this will only lead to conversations with those associates who have fallen behind their peers. That is only right and proper given the incredibly hard work a significant number of associates have put in over the past year."

The firm revamped its bonus structure in 2006 to bring in profit-linked bonuses for associates with two years' post qualification experience onwards.

The news comes after magic circle peer Slaughter and May increased the bonuses it pays to its fee earners and staff last December having brought in a new merit-linked appraisal process for its associates.