California's elections watchdog is poised to force groups that hire lobbyists to reveal more about hundreds of millions of dollars spent to sway state lawmakers on climate change, education and other issues.

In 2015, spending on lobbyists in the most populous U.S. state topped $243 million – nearly as much as the payroll for all of California's lawmakers combined.

"We want more disclosure of these payments to shine light on the interaction between public officials and the special interests attempting to influence them," said Jodi Remke, chair of the California Fair Political Practices Commission, which is set to vote on the new rules on Thursday.

California joins a handful of states considering tighter campaign finance and ethics laws in the run-up to the November election, including Missouri, New York, New Mexico and South Carolina. The California rules would not apply to federal lawmakers, such as the state's U.S. representatives.

If the rules are approved, organizations that hire lobbyists would have to specify whether payments over $2,500 are used for advertising, research, event planning or public affairs, among other categories.

But critics say the proposal does not go far enough.

The new rules do not, for example, require those who hire lobbyists to identify the legislation that an individual payment was intended to influence.

And critics say the public affairs category, which encompasses grassroots organizing and coalition building, could easily become a murky catch-all much as the "other" category is used currently.

"If the idea is to improve disclosure, why create a new category that is just as vague?" asked Denise Roth Barber, managing director of the National Institute on Money in State Politics.

Lobbyists have been mostly quiet on the proposal. By Wednesday afternoon only one firm had responded to the commission's request for comment, saying the regulations would create too much paperwork and asking that the effective date be postponed until 2017.

None of 2014's top spenders on lobbying – among them the Western States Petroleum Association and California State Council of Service Employees – would comment for this article.

Remke conceded the measures are incremental, blaming an outdated software system for limiting the number of new categories that can be added to California's searchable campaign spending database.

But Carmen Balber of Santa Monica-based Consumer Watchdog said the commission could still demand more details, uploading the disclosure forms as stand-alone images or offering copies to the public upon request.

(Reporting by Sharon Bernstein; editing by Sara Catania and Cynthia Osterman)