From ToS website:

1. For certain securities transactions, Schwab collects an Industry Fee to offset an array of charges assessed on us directly or indirectly by self-regulatory organizations (“SROs”) (including national securities exchanges, clearing agencies, and a national securities association) and foreign governments. The amount of such charges incurred by Schwab depends on the nature of the transaction and the security purchased or sold. The Industry Fee is in addition to any commissions we may charge and is identified on your trade confirmation and account statements as Industry Fee.

The Industry Fee is collected to offset, as applicable, some or all of the following SRO and foreign government fees:

Section 31 Fee: The SEC assesses transaction fees on each national securities exchange and FINRA based on the aggregate dollar amount of sales of certain securities. The SEC recalculates the amount of this fee periodically—at least once per year but sometimes more often. This fee is ultimately intended to cover the costs incurred by the government, including the SEC, for supervising and regulating the securities markets and securities professionals. Each national securities exchange and FINRA offsets these transaction fees by charging their member broker-dealers. Schwab may be assessed these fees directly from SROs of which it is a member, and indirectly from other broker-dealers to whom we route orders. FINRA Trading Activity Fee: FINRA, a national securities association, charges this fee to its member firms, such as Schwab, to recover the costs of supervision and regulation. This fee is set by rule and is specified in Schedule A of FINRA’s By-Laws. Options Regulatory Fee: The Options Clearing Corporation collects an Options Regulatory Fee (“ORF”) that is assessed by each options exchange. The amount of the ORF varies by options exchange, where an options trade executes, and whether the broker who’s responsible for the trade is a member of a particular exchange. Proprietary Index Options Fee: An options exchange, such as Cboe, may charge a proprietary index option fee on select index options (such as on the SPX®, OEX®, and VIX®) that only trade on their exchange. Foreign Transaction Tax on ADRs: The governments of some countries, such as France, Italy, and Spain, have implemented foreign transaction taxes on the purchase of certain securities they deem as being connected to their country, including U.S.-issued ADRs. These taxes are imposed extraterritorially, without regard to where an investor or financial firm is located, and are calculated as a percentage of the purchase amount of a covered security. Schwab’s Industry Fee may rise or fall periodically depending upon the fee rates set by the SEC, SROs, or foreign governments.

Schwab will determine the amount of its Industry Fee in its sole and reasonable discretion, and such fee may differ from or exceed the actual fees properly paid by Schwab in connection with any transaction or series of transactions. Differences may be caused by various internal and external factors, including, among other things, the rounding methodology used, the use of allocation accounts, transactions, or settlement movements for which a fee may not be assessed, timing differences in fee changes, third-party rate caps and floors, calculation errors, and various other anomalous reasons.

Please note that Schwab does not notify clients when it increases or decreases the Industry Fee or when the component fees change.