Social Security benefits are a major source of income for millions of retirees, with around one in five married couples depending on their benefits for at least 90% of their income in retirement, according to the Social Security Administration (SSA).

However, you may not be able to rely on your monthly checks as much as you think in the future. While the program is not going bankrupt or on the verge of collapse, benefit cuts are on the table. And there are a few signs those cuts could occur sooner than expected.

1. Mass unemployment could force the SSA to make cuts sooner

Although current benefits are not at risk of being reduced due to the coronavirus pandemic, COVID-19 could exacerbate Social Security's problems and result in future cuts.

Generally, the SSA uses money from payroll taxes to pay out current retirees' benefits. However, payroll taxes are no longer enough to continue paying out benefits in full, so the SSA has been forced to tap its two trust funds to cover the deficit. Those funds are quickly running out of money, though, and according to the SSA's most recent projections, they'll be depleted by 2034. If Congress doesn't make any changes before then, payroll taxes will only be enough to cover around 76% of future benefits.

COVID-19 could make the problem worse, however. Because Americans are facing unemployment in record numbers, there are a lot of people not paying payroll taxes right now. That means the SSA is collecting a lot less than expected in taxes and will likely need to take even more from its trust funds to continue paying out current benefits. While nobody knows exactly what this will mean for the future of Social Security, a report from the Bipartisan Policy Center estimates that because of COVID-19, the trust funds could be depleted as soon as 2028.

2. Early retirees could affect the trust funds

While the mass layoffs have affected all age groups, older workers have been hit particularly hard. Adults age 55 and older experienced an unemployment rate of nearly 10% in June, according to the U.S. Bureau of Labor Statistics, which is one of the highest jobless rates among all age groups.

If you lose your job later in life, it could be tough to find another one before you retire. And if a second wave is about to hit, there could be another round of layoffs in the near future. With no end in sight for this pandemic, there's no telling when jobs will be readily available again.

For that reason, older unemployed workers may simply choose to retire early rather than look for another job. They may also decide to claim Social Security earlier than they'd planned, which means there'll be more money the SSA will need to take from its trust funds. Between receiving less money in payroll taxes and paying out more in benefits, that could result in the trust funds running dry sooner and benefit cuts happening earlier than expected.

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Pictured, the Social Security Administration offices just off the 16th Street Mall in Denver, Jan. 30, 2015. Craig F. Walker / The Denver Post

3. Payroll tax cuts could reduce future benefits

As part of the next coronavirus stimulus package, President Trump is proposing payroll tax cuts. While that may be good news for current workers, it could spell disaster for Social Security.

Payroll tax cuts would reduce the amount the SSA has to pay out in benefits right now, meaning it would need to take even more from its trust funds. In addition, it would mean that once the trust funds are depleted, the SSA will have less money to pay out in future benefits. Right now, payroll taxes are expected to cover only around 76% of future benefits. If taxes are cut, benefits may need to be reduced even more.

Preparing for an uncertain future

There's no guarantee that any of these things will happen, but if Congress doesn't come up with a solution, benefit cuts are a real possibility. Because nobody knows what will happen, it's a good idea to plan on benefits being reduced as you're preparing for retirement.

Social Security benefits are designed to replace around 40% of your pre-retirement income, but you may want to assume they'll make up an even smaller portion of your income in retirement just to be safe. Try your best to beef up your retirement fund now because you may need to rely on your personal savings for the bulk of your income in your senior years.

You can also consider delaying Social Security benefits because that will result in bigger checks. If benefits are cut in the future, that extra money each month can serve as a cushion.

No matter how you choose to prepare for retirement, make sure you have some type of Social Security strategy in place. Even if benefit cuts don't happen, it's better to be prepared, just in case.

This article originally appeared in The Motley Fool. The Motly Fool has a disclosure policy.