Wells Fargo & Co.’s grip on the U.S. mortgage market has tripped alarms among regulators and lawmakers concerned that the bank’s control over one of every three new loans could hurt consumers and undermine markets.

Wells Fargo and its two largest rivals, JPMorgan Chase & Co. and U.S. Bancorp made half of all U.S. home loans in the first six months, according to Inside Mortgage Finance, an industry publication. Wells Fargo alone controlled 33.1 percent. In mortgage servicing, which involves billing and collections, four firms have 50 percent of the business, and Wells Fargo is No. 1 in that field, too, with 18.5 percent.