By Valentina Za and Giuseppe Fonte

ROME (Reuters) -Italian Prime Minister Giorgia Meloni's party has filed a new proposal to protect borrowers if they fall behind in repaying their bank debt, another move that investors said stoked risks for the country's 307 billion euro ($328 bln) bad loan market.

Italian lawmakers upset bad loan investors last month by proposing to give borrowers the right to repay their original loan at the discounted price at which the creditor bank sold it on, plus a 20% premium. To dispel concerns, Meloni said on Sept. 7 that there were no measures "on the launch pad" for non-performing loans.

However, lawmakers from Meloni's own Brothers of Italy party have now put forward to parliament another rule that would make it easier to apply their initial proposal.

"The latest amendment aims to help borrowers to buy back loans," senator Renato Ancorotti, one of the promoters of the measure, told Reuters.

The proposed changes would make it obligatory in banks' sales of bad loans to include in contracts the price of individual loans, even if they are sold in bulk.

As a consequence, investors could act in court to recover soured loans from borrowers only if the contracts comply with the new requirements.

A preliminary discussion on the proposal, which would be introduced by amending a government decree that in August imposed a surprise one-off tax on bank profits, is expected on Wednesday in the upper house committees.

In a bulk sale of credits, the relevant price for the market is that of the overall portfolio, which is an average of the single loans' prices.

Portfolios can comprise thousands of loans, which would make it too onerous to price each individual loan properly.

Three bad loan investors said the market did not expect the latest measure from Brothers of Italy to go through but it would create problems if it did.

Attempts to change the rules of the game with retroactive effect are perceived as damaging, the people said requesting anonymity given the sensitivity of the issue.

The rule sets a three-month limit to amend transactions that have already taken place but investors said it was impossible to retroactively price single loans in a meaningful way.

($1 = 0.9361 euros)

(Editing by Keith Weir)