As head of Medef she wields more power than some cabinet ministers and has led prickly negotiations with trade unions to address what many, from independent economists to President Francois Hollande, consider a major reason for France's loss of industrial competitiveness - high unit labour costs and inflexible work practices.

But in a move that has infuriated some at the top of the French business world, the diminutive 53-year-old wants to tweak Medef's statutes so she can run for an unprecedented third term.

Parisot faces a crucial first obstacle on Thursday when she must persuade Medef's executive committee to allow her to stand, but then she must also get a two-thirds majority at a general assembly in late April to change the rules.

In response to accusations that she is engineering a permanent takeover of the organisation, Parisot, who in January persuaded three trade unions to back a revamp of France's rigid labour rules, says she needs more time to complete her work.

"Everyone, even my rivals, say I have done a good job. So how can I at the same time be accused of being a dictator?" Parisot said at her monthly news conference last week.

"Mrs Merkel can stand as many times as she wants. In most Western democracies there are no term limits," she added.

The comparison with the combative German chancellor is a telling insight into Parisot's style over two terms since 2005 in one of the most politically charged roles outside government, sometimes dubbed the "boss of the bosses".

A skilled speaker and frequent television guest, Parisot has eclipsed challengers within the federation to become its single voice to the outside world, with Medef insiders also testifying to the tight grip she keeps on its internal policymaking.

The head of its ethics committee has already resigned in protest at her call to scrap the two-term limit.

While the outcome of the leadership battle remains hard to predict, at stake is whether Medef will back Parisot and her method of seeking gradual consensus with unions, or go for a candidate who might push for more radical reform.

DOUBLE SEDUCTION

Heiress to the 77-year-old Parisot furniture group, Parisot skipped a life selling beds and desks to study law and political science before taking over France's influential IFOP opinion and corporate strategy group.

Her arrival at the head of Medef in 2005 marked a break in style from predecessor Ernst-Antoine Seilliere, 21 years her senior, whose "Baron" nickname reflected his stiffly patrician bearing.

"The sight of this young woman coming in really freshened up the image of the employers' federation," one former senior Medef official said of Parisot, with her modishly short haircut and passion for street art.

"She set about her work with two preoccupations: to seduce public opinion and seduce the political power of the day," said the official, who would only talk on condition of anonymity.

She raised eyebrows in 2011 by co-authoring a book attacking the extreme right of Marine Le Pen, something that may have won her favour with the conservative government at the time but drew criticism that she was straying from her proper role.

Barely concealing her preference for ex-president Nicolas Sarkozy in last year's election, Parisot is a staunch critic of the Socialist Hollande, attacking the tax hikes in his 2013 budget, which she says strangle investment and innovation.

Yet she has cooperated with Hollande, delivering a January 11 agreement with unions that will form the basis of his planned labour reform by trading off greater protection for short-term contracts with more flexible hire-and-fire rules.

If the reform passes parliament in the weeks ahead, it will be a modest step towards the kind of "flexi-security" model that has allowed Denmark and others more wiggle room to adjust their workforces to the ups and downs in the economy.

READY FOR BATTLE

Some argue, however, that it is simply too modest.

"It's okay. It is not a historic accord," Pierre Gattaz, chief executive of electronics components group Radiall SA and a declared challenger to Parisot, told Reuters.

"The problem is that our country has not yet accepted the basic rules of globalisation," said Gattaz, whose book "Seven Pillars of Growth" argues for deeper reforms to reverse the decline in the French economy.

Campaigning in earnest will only start when it is known whether Parisot can get the rules changed. For now Gattaz and other potential candidates are appealing to Parisot to back down from a move they argue could tear the organisation apart.

"There is no chance she can change the statutes," insists Thibault Lanxade, head of payment services group Aqoba, arguing that the federation's large construction, industrial and public sector branches were among those opposed to the change.

"There is a huge risk that this is going to ruin the image of the organisation. Laurence is a fighter, but this is one fight too many," Lanxade, also one of the handful of likely contenders, told Reuters.

Yet Parisot, whose hand was last week strengthened by an opinion issued by Medef's statutes committee that a rule change was technically possible, appears to relish the fight and has challenged rivals to an open debate on policy.

"Obviously some people are scared of going head-to-head in an election," she told reporters. "I am the one taking the risks here, and yet I am not a bit afraid."

(Additional reporting by Emmanuel Jarry; Editing by Will Waterman)

By Mark John