French police have raided the lower house of parliament in an investigation into whether the wife of the presidential candidate François Fillon was paid for an allegedly non-existent job.

The unusual step, requiring authorisation of the speaker of the lower house, was carried out as part of an inquiry into the “Penelopegate” scandal. It was not immediately clear whether Fillon’s own office was being searched.

Investigators are looking into possible misuse of public funds after a newspaper alleged that Fillon’s Welsh-born wife, Penelope, was paid €500,000 (£430,000) over eight years as his parliamentary assistant for work she did not perform. It is not illegal for French politicians to employ spouses or members of their family, but there is an obligation for them to carry out the job.

Fillon and his wife were questioned separately for five hours on Monday by anti-corruption officers. France Inter radio suggested police were searching for her employment contracts.

Fillon has said he is the victim of a smear campaign. In a French television interview, he insisted his wife’s work had been “real and legal”.

On Monday, parliamentary allies from the rightwing Republicans party said they were giving their full backing to their presidential nominee. “He has the unanimous support of the lawmakers,” said Christian Jacob, its leader in the lower house.

The allegations have put pressure on Fillon, who had styled himself as sleaze-free and had been considered a frontrunner for the presidential election this spring. Recent polls have indicated support for Fillon falling slightly. He is slightly behind the far-right Front National’s Marine Le Pen, with Emmanuel Macron, the maverick independent centrist, breathing down his neck.

On Tuesday the European parliament said it was asking Le Pen to start repaying about €300,000 it said were wrongly paid to legislative aides.

An EU parliament letter to Le Pen gave Tuesday as the deadline to begin repayment. Failure to do so would result in her monthly EU parliamentary salary cut by half to €3,000 from Wednesday. She would also lose other allowances. In total about €7,000 would be deducted from her monthly EU salary, an EU official said.

The request follows the European anti-fraud office’s findings that some of Len Pen’s aides were paid from the European budget while actually working as her cabinet chief and bodyguard, breaking the parliament’s rules. She has denied any wrongdoing.