The case is being brought by Massachusetts-based firm NewRiver, which contests that Morningstar used "screen scraping" technology to copy thousands of documents from its database for use with its own products.
NewRiver's web-based service, which can cost up to $500,000 a year for subscribers, checks the Securities and Exchange Commission's Edgar site for new mutual fund prospectuses and stores them in its database for brokerage houses to access.
The company, which processes around 1,000 documents a night, says that between May 1st and December 3rd 2008, Morningstar accessed its database over 130,000 times using internet addresses traced to Chicago and China.
A Morningstar spokeswoman denied that the company had used NewRiver's technology or data, or that it had accessed its password-protected sites to create its products.
"We think the lawsuit has one purpose: to discourage Morningstar from competing with NewRiver," she said.
NewRiver launched in 1987 and it patented its online prospectus service in 1998.