MONTREAL -- Construction magnate Tony Accurso, a key figure in Quebec's ethics scandals, was arrested Thursday for the second time in months as police continued their crackdown on alleged corruption.

The RCMP says four men, including Accurso, were arrested and faced six charges each including fraud, conspiracy and corruption.

The men are accused of concocted a 17-point "Plan of Action," with help from inside the Canada Revenue Agency, to defraud the taxman of more than $3 million. Police said the plan involved one numbered company, a fake company, and false documents.

The other accused are: Francesco Bruno, also a construction owner; Francesco Fiorino, an accountant; and Adriano Furgiuele, once an auditor at the revenue agency. A fifth suspect is still being questioned by police.

Accurso was arrested and charged with separate crimes in April, including fraud, conspiracy and breach of trust. His alleged ties to Montreal politicians helped kick off a wave of corruption scandals more than three years ago, which are now the subject of a public inquiry.

Alleged impropriety in the construction industry has also become a key issue in the current provincial election campaign.

Accurso's arrest forged its way into the campaign when Liberal Leader Jean Charest was questioned on Thursday about its timing.

The arrest occurred one day after a TV report that said police stopped shadowing a construction businessman after he was seen chatting with the premier at a public event. Charest has reacted angrily to that report, calling it a smear by association.

He said he has never interfered with police work -- and he cited the Accurso arrest as a case in point.

"You have there an example of decisions that are made by police authorities," he said in Quebec City.

"They may have 1,000 reasons why they choose to do an operation at one point in time, whatever the circumstances may be."

The construction boss was arrested at his home after an early-morning bicycle ride.

Charest was asked whether he was concerned that Accurso-owned companies could still manage to obtain contracts in the premier's much-vaunted Plan Nord aimed at developing northern Quebec.

"In the case of Mr. Accurso's businesses, there are laws we have brought in, in particular to be able to deal with companies that have committed fraud and to restrict their ability to do business with the government of Quebec," he replied.

"And those laws apply to Mr. Accurso's businesses. If they find a way to get around that law, if there are loopholes in the law, we'll deal with the loopholes also."

The accused are to appear in court in September.