Share prices for Visa Inc. and MasterCard Inc. have drawn investor interest so far this week as lawmakers worked toward a compromise that would protect transaction fees they charge to banks.

The regulatory reform bill would empower the Federal Reserve to set fees for merchants that are "reasonable and proportional" to the cost of processing debit transactions.

"Visa and MasterCard still may have to cope with some business-model changes, but these would likely be less than had been feared," Jason Kupferberg, an analyst at UBS AG, wrote in a note Monday.

Under a compromise between the House and Senate, the Fed will not be able to regulate "network fees" that Visa and MasterCard charge to banks, according to Sen. Richard Durbin, the Illinois Democrat who drafted the interchange regulation amendment.

Visa shares closed at $80.90 Monday, up 5% from Friday, and MasterCard climbed 4.2%, to $223.34. Midday Tuesday, MasterCard shares were up 0.89%, to $225.33, though Visa slipped 1.48%, to $79.70. Shares of both companies had fallen about 14% since May.

Payments companies have voiced strong objections. "We continue to have concerns that the ultimate outcome of this legislation would be the passing of merchant acceptance costs to consumers," MasterCard spokesman James Issokson said in an e-mailed statement.

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