Breaking this down (and agreeing with previous comments and observations),
The company sponsor a 401(k) plan for all employees.
All of the field employees get a $4/hour non-elective employer profit sharing contribution to the plan. The profit sharing plan is tested for nondiscrimination (since non-field employees do not get $4/hour NEC and the amount of contribution for field employees varies based on hours worked). The nondiscrimination test supposedly passes.
The company wishes to offer to the field employees the option to continue receiving the $4/hour NEC or receive $3 in direct compensation. This clearly is considered a cash or deferred arrangement (CODA) going back to the 1950s when Kodak offered employees the right to take their profit sharing amount in cash or have it contributed to the plan. In this case, put another way, a field employee can choose to receive $3/hour in direct compensation, or get a $3/hour amount deferred into the 401(k) plan and get a $1/hour match contribution. There is not enough information to know how this deferral and match interacts with the provisions of the existing 401(k) plan. The 401(k) plan's eligibility to make elective deferrals, any existing match, match allocation eligibility requirements, vesting and other similar BRFs would need to be reviewed. The 401(k) plan also would need to consider what happens should a field employee reach the 402(g) annual deferral limit during the plan year. There would be no opportunity to deposit the $3/hour deferral into the plan without violating 401(a)(30) limits.
A guess as to the motivation for considering this idea is that enough field employees want cash-in-hand now, even at the cost of $1/hour off the top and paying payroll and income taxes. The company likely is looking at its portion of payroll taxes plus any impact this may have on other company-provided benefits.
As a possible compromise, the company could consider keeping the current $4/hour NEC and making in-service withdrawals as readily available as permissible. For example, these amounts could be withdrawn from the plan once they have been in the plan for at least 2 years. The amounts also could be available if the participant, for example, has at least 60 months of participation, or attained Normal or Early Retirement, or is disabled, or has a safe-harbor or non-safe-harbor hardship. This avoids all of the payroll tax issues, doesn't complicate the 401(k) plan design, apparently already passed nondiscrimination testing, does not involve a match, and cannot trigger 401(a)(30) limits. Once an employee is qualified for in-service withdrawals under any one of these rules, the employee would have access to the funds.
Generally, we don't advocate very liberal in-service withdrawal rules and would recommend limiting the number of withdrawals per year, but if the recordkeeper is geared up for plan accounting for new features like emergency savings, qualified disaster, qualified adoption and all of the other available in-service forms of payments, this approach should be relatively to implement.