WASHINGTON -- President Barack Obama on Monday dropped in on a White House press call to urge the Senate to pass legislation that ensures women are paid the same amount as their male counterparts.

"Tomorrow, Congress is going to have a chance to vote on the Paycheck Fairness Act," Obama said on the call, during which he spoke for just a couple of minutes. "I don't have to tell you how much this matters to families across the country. All of you are working day in, day out, to support the basic principle, equal pay for equal work."

The White House gave only about an hour's notice that Obama would personally take part in the call, which comes a day ahead of a key Senate vote on the Paycheck Fairness Act. The bill would require employers to demonstrate that any salary differences between men and woman doing the same work are not gender-related. The bill would also prohibit employers from retaliating against employees who share salary information with their co-workers, and would require the Labor Department to step up its outreach to employers in order to eliminate pay disparities.

On average, women in the U.S. still make 77 cents for every dollar that men make in the same job, said senior administration officials on the call. The rate drops even lower for minorities, to 64 cents for African-American women and to 56 cents for Latinas.

"Congress has to step up and do its job," Obama said. "Women are the breadwinners for a lot of families, and if they're making less than men do for the same work, families are going to have to get by for less money for childcare and tuition and rent ... Everybody suffers."

The president added that he plans to release a formal administration policy message in support of the bill later Monday.

The White House call was just the first in a series of press calls taking place Monday on the issue. Reps. Jan Schakowsky (D-Ill.) and Rosa DeLauro (D-Conn.) are holding a call to pressure Mitt Romney to take a stand on the issue. Sens. Barbara Mikulski (D-Md.) and Charles Schumer (D-N.Y.) are also teaming up with White House senior adviser Valerie Jarrett on another call to urge passage of the bill.

Jarrett joined Twitter earlier Monday and made the Paycheck Fairness Act the subject of her first tweets. She was asked almost immediately by a Twitter follower if she is paid as much as her male counterparts in the White House.

"Indeed I am. Same pay as the other senior men in the WH," Jarrett tweeted back.

CORRECTION: This story previously incorrectly stated that Rosa DeLauro is a congresswoman for California, rather than Connecticut.