BRUSSELS (Reuters) - European campaigners against an EU-U.S. accord have held up progress towards the world's biggest free trade deal by deluging an online public consultation that EU officials had hoped would help them unblock a key issue.

Of almost 150,000 submissions to the public forum on how to protect businesses from unfair government interference, over 95 percent were from supporters of a small group of organisations hostile to a deal with Washington and who submitted identical or very similar responses, two EU officials have told Reuters.

Investor protection is among the most contentious issues in the proposed EU-U.S. trade pact because Europeans fear U.S. multinationals would use the investor-to-state dispute settlement (ISDS) mechanism to challenge food and environmental laws in the EU on the grounds that these were restricting free commerce.