Consob, the Italian stock market regulator, banned short-selling of Finmeccanica shares on Tuesday and Wednesday after the company’s shares fell more than 10 percent in early trading. The stock closed down 7.3 percent on Tuesday. A short sale is a bet that a company’s stock will fall.

The case puts the company, which is in the middle of a critical restructuring, in a difficult position. A board meeting is expected to be called soon to discuss whether to appoint an interim chief executive.

Whether the various corporate investigations will have any effect on voters, they are creating a political stir. In the case of the bank Monte dei Paschi di Siena, known as M.P.S., the investigation has focused attention on the role played by the Bank of Italy and its former chairman, Mario Draghi, who is now president of the European Central Bank. Mr. Draghi asserted last week that the Bank of Italy had “done everything it should” with respect to M.P.S., adding that much of the criticism was “part of the regular noise that elections produce.”

The M.P.S. imbroglio has also given the former prime minister, Silvio Berlusconi, an issue with which to attack his political enemies as he angles for a comeback. The bank is based in Siena, in a part of northern Italy that is a stronghold of the leftist Democratic Party. Mr. Berlusconi, a conservative who hopes to be a spoiler in the elections this month, has been trying to place blame for the scandal at the Democratic Party’s doorstep.

But Mr. Orsi, the Finmeccanica chief, is said to be connected to a conservative party, the Northern League. And on Tuesday Mr. Berlusconi denounced the recent actions by prosecutors, including the investigation into the helicopter deals with India, which were made when he was prime minister.

The Italian news agency ANSA quoted Mr. Berlusconi as saying “everyone knows” that the deal involved agreements between governments.

“The fact that there is the risk of magistrates intervening I consider to be economic suicide,” he said, referring to the local investigation in Milan.