7. EMPLOYEE BENEFITS

Pension Plan

We maintain a qualified defined benefit pension plan (“Pension Plan”), which covers eligible current and former employees and has been frozen since March 31, 2009. No new participants may enter the Pension Plan and no further benefits will accrue. However, years of service continue to count toward early retirement calculations and vesting of benefits previously earned.

We also have a limited number of supplemental retirement plans to provide certain key current and former employees with additional retirement benefits. These plans are funded on a pay-as-you-go basis and the accrued pension obligation is largely included in other long-term obligations.

The elements of retirement benefit expense are as follows:


	Three Months Ended
	March 31,		April 1,
(in thousands)	2019		2018
Pension plans:
Interest Cost	$	20,521	$	19,788
Expected return on plan assets		(21,502)		(22,624)
Special termination benefits		6,834		—
Actuarial loss		5,525		6,295
Net pension expense		11,378		3,459
Net post-retirement benefit credit		(651)		(681)
Net retirement benefit expenses	$	10,727	$	2,778

Early Retirement Incentive Program

In February 2019, we announced a one-time voluntary Early Retirement Incentive Program (“ERIP”) that was offered to approximately 450 employees. The ERIP allowed them to accept a special termination benefit based on years of continuous service and the option to take their vested benefits under our frozen Pension Plan in a lump sum payment. Nearly 50% of the eligible employees opted into the program.

Lump sum pension and termination payments made under the ERIP totaled approximately $35.1 million, decreasing both the benefit obligation and the fair value of plan assets. Due to the significance of this program, we remeasured the retirement plan assets and benefit obligations as of March 22, 2019, using a discount rate of 4.10% and an expected return on plan assets of 7.75%. The remeasurement and the special termination benefits resulted in a net reduction to the pension liability of approximately $13.1 million and the recognition of a one-time non-cash charge of $6.8 million for the special termination benefits, presented in retirement benefit expense on the statement of operations during the three months ended March 31, 2019. Our unfunded liability for the Pension Plan was $535.1 million as of March 31, 2019, compared to $548.2 million as of December 30, 2018. These are included in pension and postretirement obligations on the statements of operations.

401(k) Plan

We have a deferred compensation plan (“401(k) plan”), which enables eligible employees to defer compensation. Our matching contributions in the three months ended March 31, 2019, and April 1, 2018, were $0.6 million and $0.7 million, respectively, and are recorded in our compensation line item of our condensed consolidated statement of operations.