Hundreds of us-listed companies, including coca-cola, procter & gamble and ford, have come out against a proposal from the securities regulator that would shield the vast majority of hedge funds from disclosing their stock market holdings.

A total of 381 companies on monday signed a letter, organised by the new york stock exchange, saying the securities and exchange commission proposal would deal a debilitating blow to investor relations.

The proposed rules governing so-called 13f filings would relieve all but the worlds largest 550 investment managers from disclosing their public equity holdings.

This would allow most hedge funds to keep their portfolios secret, including activist investors who could quietly build up stakes of target companies.

The proposal limits access to information for public issuers and investors, which is the exact opposite direction of where the commission should be heading, the letter stated. the proposals limitation on transparency is at odds with the commissions regulatory agenda in general and with how the commission itself has explained access to information and its role in facilitating such access.

Smaller companies in particular would be hurt, it argued because they would lose visibility to a higher proportion of their investor base than larger groups, making them more vulnerable to activists.

The reduced transparency would deliver a debilitating blow for investor relations teams who lead shareholder engagement for public issuers and are in constant search for information regarding the owners of their companies, the letter said.

Under the sec plan, only investors with assets of more than $3.5bn will have to submit quarterly 13f filings, raising a threshold that is currently set at $100m. jay clayton, sec chairman, said the aim was to reduce unnecessary burdens on smaller fund managers.

The nyse suggested that the sec form a working group of public companies, investors and academics to recommend alternative changes to the 13f filing. the sec declined to comment.

The group arguing against the changes included many of the biggest companies listed in new york from a cross-section of sectors including health insurer cigna, logistics giant fedex and retailers home depot and macys. foreign companies with listings in the us, including bp, the oil major, and alibaba, the ecommerce group, also signed.

But the letter omitted a number of high-profile names, including warren buffetts berkshire hathaway, jpmorgan chase, johnson & johnson and visa.

The proposal has attracted other detractors, including allison herren lee, the secs only democratic commissioner. in july, she said the plan joins a long list of recent actions that decrease transparency and reduce both the commissions and the publics access to information about our markets.