During a debate on the labour reform on Thursday evening, Communist senators accused Pénicaud of profiting from a decision to shed 900 jobs - 233 of them in France - while she was Danone's head of human resources four years ago.
On 30 April 2013 Pénicaud made a profit of 1,129,034.54 euros in one day by exercising her right as a member of Danone's board to buy 55,120 shares, then selling them as their value soared due to the announcement of the redundancy programme, Communist Party paper l'Humanité has revealed.
She kept hold of a further 2,900 stock options.
"This point is extremely serious from an ethical point of view and perhaps from a legal one," Communist Senator Eliane Assassi declared. "Because as part of your responsibilities you drew up this redundancy programme and you took its fruits for your personal profit."
The revelations came as the government was drawing up plans to "tighten our people's belts by several notches", Asssassi said.
"We're here to make the law, not to spread demagogic approximations about individuals," Pénicaud replied.
The minister has also come under fire because of an investigation into alleged favouritism relating to a trip to Las Vegas by President Emmanuel Macron when he was economy minister and she was head of the body that awarded the contract to organise it.
The Senate went on to agree to the fast-tracking of labour reform with the Communists and Socialists voting against.
Despite union opposition, with a day of protest planned on 12 September, the proposals will be presented to parliament in the autumn.
Clean-government changes approved
Meanwhile in the lower house, where MPs were debating a bill on politicians' ethics, Danielle Obono of the left-wing France Unbowed party, brandished the Communist paper and suggested her colleagues read about "activities that, I think, we should prevent".
Her party has called for the bill to tackle the world of finance as well as cleaning up political practices.
Despite some angry exchanges over the chairing of the session, MPs voted in favour of ending their 5,373-euro expense allowance - along with 6,110-euro allowance for senators - replacing it with a requirement to claim and submit receipts.
Although abuses of the allowance have come to light, such as its use to pay for family holidays or the purchase of a television, some right-wing MPs were unhappy with the change, claiming it might hamper their ability to do their jobs and lead to a "grand inquisition".
They also backed an amendment to prevent political parties charging interest on loans.
The measure is mainly aimed at the far-right National Front, which is currently under investigation for selling campaign packs to election candidates, who bought them with money borrowed from a party-linked body.
Since the election expenses of parties that receive more than five percent of votes are reimbursed by the state, investigators say they party was effectively earning interest from taxpayers' money.