MONTREAL — Embattled Quebec construction magnate Tony Accurso announced Tuesday that he's quitting his executive posts at his billion-dollar empire, rocked by corruption allegations and tax fraud.

In a letter to employees at Construction Louisbourg Ltd., Accurso mentioned the "turmoil" surrounding the group of companies that he has run for 30 years.

He has been arrested twice this year, once for alleged tax evasion and again for alleged fraud.

The sight of Mounties leading Accurso into a precinct, bound in handcuffs, capped three years of damaging publicity for his empire.

Accurso's name also came up this month at the Charbonneau Commission that's probing ties between construction firms, government and the Mafia.

Former excavation contractor Lino Zambito said Mafia don Vito Rizzuto once mediated a dispute between him and Accurso.

He denied the mob links but acknowledged the crisis in his letter to staff.

"I assure you that I'm disappointed about the turmoil in which the Group has found itself in recent years," the entrepreneur wrote in the two-page letter.

Accurso also expressed regret at the "worries and repercussions caused to each of you."

He took over his father's construction firm of 75 staff in 1982 and has since spun a dizzying web of 63 companies worth at least $1 billion.

Accurso told staff that his firms have been "the envy of many entrepreneurs, in Quebec and elsewhere" but his business practices have landed him in hot water recently.

Earlier this month more than 90 tax investigators carried out multiple raids on Accurso's companies in the second tax operation targeting the empire in the past three years.

Construction Louisbourg and Accurso's other big firm, Simard-Beaudry Construction Inc., had previously been cited in 2010 for $4.1 million in back taxes.

Accurso also made headlines in 2009 after several Quebec politicians were found to have vacationed on his 120-foot luxury yacht.

The luxury excursions ramped up interest in his group of companies, which are involved in many of Quebec's biggest construction projects.

They include the $6.5 billion Romaine River hydro dam as well as the $2.3 billion McGill superhospital that will be the largest in Canada when it opens in 2015.

The superhospital project became embroiled in controversy last month when anti-corruption investigators raided the hospital's downtown administrative offices for alleged contracting irregularities.

A media report revealed that Accurso has landed $1 billion in public contracts since 1990, mainly from Transport Quebec.

The flood of allegations led Quebec to cancel 17 contracts worth $21.2 million that had been held by Accurso's companies.