Drain Problem-Anyone know what should be done?

When my washing machine empties the water backs up slightly in my kitchen sink but not in the bathtub, bathroom sink or toilet that are lower. Everything is on one floor. It is worth noting that an AC condenser pump and the washer empty into the same drain pipe in the utility room, but there is only a small amount of condensate pumped down the pipe at any given time. If I stop the washer midcycle when pumping out, the water does not come up the sink. Anyone know what should be done before calling a plumber?

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