Originally Posted by xliioper

Yes.
https://www.delta.com/content/www/en...es.html/#terms

"Not combinable with certificates, eCredits, vouchers, or with any other discounts. Tickets purchased with full or partial Pay with Miles redemptions are eligible for Global or Regional Upgrade Certificates but not eligible for mileage upgrades."

Originally Posted by jdrtravel

Yes, and this is strictly enforced. Last year I had a sizable e-credit that was going to expire soon, plus a companion cert that was going to expire soon. I tried to push with phone agents and supervisors, but no luck.