A government watchdog group on Tuesday said health plans across the country have not followed rules that are intended to prevent federal subsidies from being used for abortions, fueling a new GOP attack against ObamaCare just weeks ahead of the midterms.

In a sample of 18 insurers nationwide, all but one allowed women to pay for abortions through their healthcare plans, regardless of whether they are receiving federal subsidies, the Government Accountability Office found after a seven-month investigation.

The findings come at a crucial time for Republicans, who have continued to mount challenges of ObamaCare as they seek control of the Senate this fall.

The issue lies with the complicated — but crucial — way that insurers bill patients for abortions.

As part of a key compromise in the Affordable Care Act, a woman must be charged separately for an abortion to ensure that any federal subsidies she receives will never mix with abortion payments. If the payments are not separated, Republicans argue that tax money is essentially funding abortion services, even if a woman pays her own premiums.

The report does not say how many abortions were funded in this way.