Service Employees International Union is circulating a petition urging Congress to lift the cap on Social Security contributions for the wealthy.
"On April 17, most of America's wealthiest citizens will stop paying Social Security taxes," it said in a release.
That's because the Social Security's Old-Age, Survivors and Disability Insurance (OASDI) program limits the amount of earnings subject to taxation for any given year.
The limit changes every year based on changes in the national average wage index. For earnings in 2014, the base in $117,000.
"Once the payroll contribution cap of $117,000 is reached, millionaires and billionaires stop paying into the system, while the vast majority of Americans pay on all of their salary—all year long," SEIU said.
"It is time to make the 1% pay the same rate as the rest of us."
With 2.1 million members in the United States and Canada, SEIU is one of the fastest growing unions in the Americas.
SEIU is focused on uniting workers in public services, healthcare and property rights.