Money-market fund companies have doubled lobbying efforts to convince regulators and lawmakers that they aren't a threat to the financial system. The money may have been well-spent.

The 10 biggest money-fund managers and the Investment Company Institute trade group reported combined lobbying spending of $16 million in the first half of 2012 and $31.6 million last year in disclosures that reference money-market mutual funds, according to a review of documents by Bloomberg News. That compares with $16.7 million in all of 2010.

The companies are seeking to block new rules championed by Securities and Exchange Commission Chairman Mary Schapiro that are headed for a vote before a divided commission as soon as this month. The proposal would force funds to abandon their fixed $1 share price or introduce withdrawal limits and capital buffers. Schapiro can count on only one supporting vote from the other four commissioners, even as Federal Reserve officials have said that failure to enact tougher rules will leave the $2.5 trillion industry vulnerable to investor runs and threaten global credit markets.