Senator Ron Wyden of Oregon, the chairman of the Finance Committee, said the still-evolving proposal would impose an escalating tax on the payrolls of large corporations, starting at 5 percent, if any of the companies’ workers earned less than a certain hourly wage. It would include what Mr. Wyden called “safeguards” to prevent companies from laying off workers and replacing them with contract employees to avoid the tax.

“While conversations are continuing, I believe this ‘Plan B’ provides us a path to move forward and get this done through the reconciliation process,” Mr. Wyden said in a statement…

It was not clear on Friday whether the tax penalty plan would qualify because if it achieved its objective of ensuring all large companies pay their workers at least $15 per hour, none of the firms would pay the tax, and federal revenues would not change.

Mr. Wyden said as part of the plan, very small businesses “with middle-class owners” would receive an income tax credit to cover 25 percent of their employees’ wages, up to $10,000 per year per employer, in an effort to incentivize higher pay at those businesses.