A Portsmouth law firm and a Portsmouth contracting firm are tangled in Supreme Court litigation after serving as each other's unhappy customers two years ago.

The high court heard oral arguments Wednesday in a Consumer Protection Act claim by the Becksted Associates construction firm against the Nadeau law firm for using alleged deceptive and coercive business practices against them.

That's just one of several lawsuits between the two companies in the past year.

Attorney J.P. Nadeau and his son, Justin Nadeau, an attorney and former Democratic Congressional candidate, won a directed verdict for the firm in Rockingham County Superior Court in 2006 dismissing the consumer protection charge. The Becksteds appealed to the Supreme Court.

Both sides agree William Becksted Sr. and his son, William Becksted Jr., were renovating the second floor of the Nadeau law firm into an apartment for Justin Nadeau. The Nadeau court brief says the Becksteds were still billing Justin for more than $39,000 after he had paid $166,000 for a project he had understood would cost no more than $100,000, and later would cost no more than $154,000.

Nadeau refused to pay the balance because he was disappointed with the cost overruns and the work he was getting. According to both sides, he sent the contractors a letter March 4, 2005, on law firm letterhead threatening litigation unless they stopped dunning him. The Becksteds hired a different lawyer and sued the Nadeau firm on March 28.

Amid these mounting tensions, J.P. Nadeau was still representing the Becksteds in two unrelated legal cases on behalf of the construction firm. The elder Nadeau had sent his client no bills between the summer of 2004 and that December. In January 2005 he finally gave them an invoice for $12,001.50. It had obvious arithmetic errors, which Becksted Sr. picked up on. The total should been around $5,000, based on the hours and hourly rate.

Becksted asked the New Hampshire Bar Association for help resolving the billing issue. The elder Nadeau found out about it, rechecked his time log, changed the billable hours slightly, and sent a corrected bill for $5,335. He soon sent a bill for another $3,234 in legal fees for the second case he was working on. Eventually the combined legal bill reached $15,000.

Attorney Philip Pettis argued the Consumer Protection case for the Becksteds. He told the high court it was improper for the Nadeau firm to keep representing them as lawyers. Pettis also noted the legal bills arrived only after the contracting dispute had flared up.

Justice Richard Galway asked why this case is any different from the average contract dispute. Pettis said the lawyers were using their position of relative power as unfair leverage. It's hard to change lawyers in the middle of litigation. He also called the incorrect billing "inflated and deceptive."

Chief Justice John Broderick said a billing error is a foolish way to intimidate someone.

"Why would you do that if you weren't innocent?" he asked.

Pettis agreed that might not have been the best tactic.

Broderick grilled attorney Anna Barbara Hantz, the lawyer for the Nadeaus, the same way.

"You're working on my house," Broderick said. "I'm representing you in a legal case. I'm trying to use the bills you owe me to get you to drop claims against me over my house. We now have a personal dispute that's not going away. Does that bother you?"

Hantz said it certainly would.

"But the Consumer Protection Act doesn't have a different standard for lawyers," she added.