Some of the loudest critics of a plan to require stockbrokers to tell clients about bonuses they receive for switching firms are not from Wall Street, but from the insurance industry.

Insurers want the Financial Industry Regulatory Authority (Finra), the Wall Street industry-funded watchdog that is pushing the plan, off their turf, they say.

The insurers' beef stems from a Finra proposal that is set for review by U.S. Securities and Exchange Commission. Finra wants investors to know of a potential conflict of interest at play when brokers change firms and ask clients to move with them: some brokers receive hefty bonuses that may sway them to suggest the move to their clients, Finra says. But those clients may not be able to hold the same securities or could incur new costs when they move their accounts to the broker's new firm, Finra has said.

The regulator's plan, filed with the SEC in March, would apply to recruitment compensation of $100,000 or more, including signing bonuses and other payments that brokers may receive later. Brokers and their firms would not have to disclose exact dollar amounts, but rather the ranges in which the compensation falls. The first range would be $100,000 to $500,000, followed by higher increments.

Some of those bonuses may be based on compensation from other financial services entities, such as insurers, that partner with brokerages to sell products to investors, according to Finra's proposal. Finra's proposal would require including that compensation in bonus calculations.

Large brokerages have generally supported the plan, saying it promotes transparency. Smaller firms, however, have said it invades their brokers' privacy and that Finra is wrong to assume a conflict exists.

But a new argument cropped up during an SEC public comment period that ended last week. Insurers are taking issue with four lines of the Finra plan that require the disclosures to include funds received from insurance firms and others. They say that is a huge overreach of authority.

Many of the 633,000 Finra-licensed stockbrokers hold additional licenses that let them sell other types of financial products or services like insurance. Some even sell products from insurers or other financial entities that are units of the company that owns their brokerage firm.

Finra's proposal places the watchdog squarely in state-regulated insurance turf, insurers say. The plan "greatly overreaches" and should be more tailored to focus on payments tied to a broker's securities activities, wrote lawyers for the Committee of Annuity Insurers, in a letter on April 18.

The coalition's 28 members include AIG Life & Retirement, a unit of American International Group Inc, and Allstate Financial, a unit of Allstate Corp. A letter from the American Council on Life Insurers, a trade group, makes a similar point.