The Senate immigration bill includes the requirement that all employers use the E-Verify system to confirm new employees' legal right to work in this country. The program has its critics.

If the Senate's version of comprehensive immigration reform becomes law, all U.S. employers will be required to use the E-Verify system to check the immigration status of new employees.

As of now, 10 states have laws making the program mandatory for certain employers, three states require all but the smallest companies to use it and five states require all companies to use it.

Having these laws on the books has provided enough real-world experiences to generate many complaints from small businesses about the program.

One is that E-Verify can only be used to check immigration status after a worker is hired, not to screen job candidates, which can lead to numerous firings.

Having to manage the system puts extra burdens on a small business's staff and its bottom line. In fact, Bloomberg Government estimates that the total cost to small business will be close to $2.7 billion.

Employers complain that the system is slow to keep up with name changes, which might prevent workers from showing up as legal residents if they've been married or divorced.

Others argue that their state's E-Verify requirements have prevented them from filling certain positions.

Even though the Senate bill is not law yet, and the House plans to take on immigration reform issue-by-issue, mandatory use of E-Verify is something that small businesses should prepare for.